Ok, so here's the solution to the riddle:
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The two unlikely eyecup-siblings were the Swarovski 8x32 EL SV and the Meopta Meostar B1 8x56. I say "unlikely" because one is nearly twice the weight of the other, they belong to different brands an have markedly different goals. Hence my surprise when I compared the eyecups and found them to be so similar than one could take them for twins (like the first answer from dorubird showed).
Personally, I find them close to eyecup perfection in shape and size. In an ideal world, there would be an ISO-standard for eyecup thread, so that you could mix-match binoculars with eyecups from other brands (who knows, there could even be a niche for a brand specializing in the manufacture of eyecups, the same way there are brands that make straps or harnesses (or the same way there are third party manufacturers of lenses for cameras, say you can buy a Sigma lens for your Nikon or Canon). But that's just daydreaming