Thanks for your reply.
Too bad - given Etymotic's approach to perfection (except for minor things such as the newer ER series' lack of clearly distinguishable side indicators and the lack of a chin-slider on the older and discontinued ER-4S' cable) and professional audio orientation, I would have expected a threaded lid that would provide even more protection and convenience in a more careless roadie/tour environment. Maybe something that could be changed in the future.
@EtyDave
Then again, it is at least nice to see that Etymotic didn't go for a very boutique- and premium-looking but less protective carrying case like it is unfortunately the trend with some companies (artificial fur on the inside that will just create more micro dust, lids that don't fully close and therefore allow moisture and dust to enter, "flaps" on the inside that look nice and keep the lid open when the case is opened up but drastically limit interior space, and other nonsense that I have seen over the years).
Sure, it's rather unlikely that a snap-on lid would fail over time (although I've had some very rare cases of cases whose lids were fitting just a bit too loosely and could theoretically pop open unintended), and my Ultimate Ears Triple.Fi 10s' case still does its job sublimely after all of those years, but nonetheless a threaded lead would have been one step closer to overall perfection.