The NACC region (and for that matter Europe and maybe Australia) are weird in the sense that their is such a high density of ornithologists, both professional and amateur, and such a long history of work in these regions, that I don't think any one committee necessarily is going to have a monopoly on knowledge. I was thinking more along the lines of places like many areas in Africa or or Asia.
It is interesting that Europe's taxonomy now seems perhaps rather static with few areas of contention. We have had our splits and lumps (e.g. Eastern and Western Olivaceous Warbler, Moltoni's Warbler etc.), and there are a few in progress (proposed lumping of Yelkouan and Balearic Sheawater, the ongoing treatment of Redpolls etc.). However, and perhaps wrongly, it feels that changes in Europe generally reach global consensus quite quickly, whereas taxonomy in the USA has more lingering issues - how long now have IOC now recognised the split of Franklin's Grouse, Green-winged Teal and Audubon's Warblers, in contradiction to Clements?
As you say, with good ornithologist on both sides of the Atlantic, it seems slightly strange that consensus has not been reached on some European and American species - perhaps again local expertise is not the key factor and it is all about scientific principle (and potentially a divide of opinion, or even regional expectations for burden of proof).
If a British Taxonomic Committee existed it would probably have just a few issues to consider - Red Grouse, Scottish Crossbill and those damn Redpolls! Apart from that it would be mainly rarities (Yelkouan Shearwater, Turkestan Short-toed Lark and the like), but I would perhaps argue that a British committee may not be the most versed in central Asian lark taxonomy. I mention the lark in jest, because (following the IOC split of Lesser Short-toed Lark), the BOURC has recently been deliberating on inclusion of Lesser Short-toed Lark on the UK list - the sole record is now judged to not be attributable to any one of the 'new' species, so the species has been removed from the British list. The lucky few who saw the 1-day Dorset bird, will now be cursing the IOC split!
Interesting, that a quick search on the web suggests that to become a taxonomist you first need a relevant degree (biology is a good fit) and then perhaps a PhD majoring in taxonomy. I particularly liked the one website that states
'Taxonomists enjoy a structured and controlled working environment. Most of their day will be spent working in offices or laboratories, with the standard risks associated with desk-based work (such as correct seating and display equipment usage).' A bit different from the tropical disease risk, biting insects, travel risks, slips trips and falls expected by the more intrepid field ornithologist!
A tour guide once told me that you can never get into the mindset of a true taxonomic specialist and that it was a whole different thing to field ornithology. If this is true, filling a local committee with ornithologists will have it's limitations.