I return alive, and with birds! I'll summarize them as follows:
Endemic birds
Socotra Sparrow: extremely common, I went to great efforts to photograph these in the city of Hadiboh only to see them every day in every location, from the ocean all the way to the highest remote peaks of the Hagghier Mountains. Very easy.
Socotra Sunbird: common. Once I learned the song and calls I was detecting them in most locations, pretty much anywhere with native habitat. Not always cooperative but I did get some decent photos a couple times. I'm sure they pose better in seasons with more food sources available, it was pretty dry and not so flowery this time.
Socotra Buzzard: uncommon, but I heard them most days, anytime we left the ocean plane and travelled up into the hills leaning into steep cliffs, plateaus, or mountains. My best view was a dark morph bird that flew by swiftly and closely but at a time where my camera was not accessible. I have mediocre photos of them from other days, mostly distant and far away.
Socotra White-Eye: uncommon. I mostly only heard this species but did get some reasonable views when birds were in an accessible spot (i.e. not high on a scrambly scree slope or across a canyon). They weren't really shy but kept in cover often, which was more a facet of the habitat at the time than any real different behaviour (versus other white-eyes which I usually see only in trees).
Socotra Warbler: I barely saw this species, and I attribute that primarily to not really knowing the call well. Late in the trip I had the calls down and found them two days in a row. My best views were on a difficult hike where I couldn't lug my telephoto lens, but I was able to pish a group in close on the second-to-last day successfully for great looks. I think it's more common than my experience suggests. Each encounter involved a travelling group of several birds, maybe I missed the memo but I expected something solitary.
Socotra Starling: TBD. I had a really hard time separating these from Somali Starling, but some starlings I encountered in the highlands sounded quite different to Somali (which does have a broad diversity of calls, regardless).
Socotra Scops-Owl: Heard every night I was camping in the mountains, finally got close enough birds in the Fermhin Forest that I could call them in with playback. Four birds all calling in audible range, two of them came in. Great views. Our trip leader insisted I did not see them and fabricated my recording of the birds I took at the time as being taken from the internet. Apparently they were "supposed to be" only found in association with date palm groves of which there were no such trees in this location. His loss, I suppose.
Socotra Grosbeak: Having not seen this bird in the first week, I was starting to get concerned. However the next day, near Hoq Cave by the coast, I heard some very interesting calls that sounded like a mix of a scaly-breasted munia and European goldfinch. It simply did not even occur to me they could be found so close to the ocean. Since then I detected the species every further day of the second week in the coastal hills and scrub. Most times I did not see them, they move around a lot and cover great distances, and the calls have decent ventriloquist qualities. I eventually had priceless views of a group of 12 birds on Diksam Plateau within 10 metres as I was scouring shallow canyons for the bunting. Great views and photos for about 10 minutes.
Socotra Cisticola: More difficult than expected. I had to use eBird to find the stake-out habitat location west of Hadiboh, in succulent coastal scrub. Here I quickly encountered 3 birds, although they were hard to observe as they typically dove into cover after their display songs. I heard one later that day while we were driving through some low grassland, but aside from that I never heard or saw this bird again. Most detected by the "zip zip zip" flight song which reminded me much of Zitting Cisticola.
Forbes-Watson Swift: Apparently I was lucky enough to visit during the only time of the year these birds cannot be found. However, I did magically find a pair of birds within a canyon in the mountains. I forced the driving entourage to stop so I could get photos, which they were not pleased about, but this ended up being my only sighting of the trip. eBird flagged it as a rare sighting. I am assuming the ID based on them being swifts (and not swiftlets), but my understanding is it's quite unlikely to be anything else. If anyone knows the field marks to confirm versus other vagrant possibilities, please let me know.
Socotra Bunting: I politely requested a driver to take me to a site for this species on one of the "off days", as I was unable to find them in Hagghier or Fermhin earlier in the trip. I realized it was a bit of a needle in a haystack situation as it was evidently past their breeding season, not that any recording of the song could be found anyway. I chased every bunting song I heard on this trip, and all were cinnamon-breasted which is very common here. The driver took me to a remote spot in the Diksam Plateau that I know a previous tour found the birds at. No unusual bunting songs heard. On the last walk through one of the canyons I encountered an immature bunting following a group of Socotra sparrows, and although I can only find information on the appearance of adults, comparing to images of immature cinnamon-breasted bunting showed me this bird was very likely to be Socotra bunting. I think at this time of year they must be at lower elevations and perhaps not singing, but there is next to no information I could find on their movements.
Non-endemics of note
Egyptian Vulture and Somali Starling: Absolutely "trash" birds. Everywhere, very common, in great numbers, and always stalking us for food during all meals of the day.
Socotra Cormorant: By the second week I had seen them multiple times off the north coast of the island at various spots. Mostly flying far out to sea. In one morning I witnessed around 50-60 birds flying east just after sunrise, I'm not sure where they were headed as I never saw them on land anywhere, even on some cormorant-y rocky cliffs that looked promising.
Bruce's Green-Pigeon: I did not know there was a "fruit pigeon" here, so I was surprised to see a multicoloured large pigeon in the Hagghier Mountains on day 2. On the last day I saw several birds at range flying between the canopy, but being fruit pigeons views were often flight-only and impossible in tree canopy.
Desert Wheatear: Having only seen northern wheatear my whole life, it was a great pleasure to see that there was in fact another species of wheatear out there in the world. Never mind the 6 species I tried unsuccessfully to find in the UAE post-trip. I'll never understand why they are so hard to find, given they aren't exactly secretive birds.
Slender-billed Gull: a mint condition bird that was apparently rare for Socotra, seen at the west end of the island. New for me, although I later saw one at my layover in the UAE accompanying a black-headed gull.
Tree Pipit: I heard a strange pipit flyover while looking for Socotra bunting. I was able to get some perched views confirming it was a short-billed and otherwise not-a-long-billed-pipit, which is very common on the island. The European birding group I encountered and showed the images to said it was "just" a long-billed pipit like any other, and not a tree pipit, which was surprising considering they must be familiar with tripit where they came from. It definitely was one, though. I think it's quite rare in Socotra.
Sooty Gull, Black-crowned Sparrow-Lark, Western Reef Heron etc are all "old hat" birds for all you global travellers, but they were my first sightings, so let me enjoy them! Or don't, I'll enjoy them anyway!!
Misses
Lichtenstein's Sandgrouse: despite this apparently being one of the most common birds on the island, and multiple attempts visiting optimal habitat at dawn and dusk, not a single person on this 2-week trip heard or saw this species. I don't think they leave the island off-season, but as to where they were hiding I have no clue.
Persian Shearwater: my (feeble at best, I'll be honest) attempts to seawatch were not productive for this or Jouanin's petrel. I wasn't really expecting good chances but you just never know.
Temminck's Stint: I was promised this was a very common wader in Socotra, but they must have left prior to my visit, or otherwise been unseasonal.
White-browed Coucal: I didn't really do research on this species in terms of the best habitats to search, but regardless, I did not encounter one.