If I use throwaway numbers: What happens if I lose access? Do I _need_ the number for anything in the future (say, device died)? Can someone else mess with me if they get access to this number, if the number gets reassigned? Searching for this kind of information is hard, because 'Signal' isn't exactly a word that search engines understand in context.
Chromium and Chrome are the same thing for me: A browser I don't care for and only install on a dev machine for some tests. I wouldn't install either on my personal rig, ignoring the suffixes. And certainly not for an 'app'. It's both 'Not liking Google' and 'No general web browser to run an IM client'. The latter isn't solved by Chromium.
As far as I'm aware there are no Google Play Services for FxOS (looking at this Flame right here) and I expect that there's no easy solution for SailfishOS either.
I understand that I'm not the target audience. Please believe me when I say that I don't feel that I can (as in, it suits me/feels okay to do so) use Signal right now. I'm writing these messages here not to hit on your work, but to express that there is an audience with other preferences/goals. It's Christmas soon, after all - consider this my public, unrealistic, idealistic wishlist.
(Edit: And I apologize that my critical comment ranks rather high right now. I might believe that I'm not completely bonkers and there are other people that feel the same way, but it still sucks to see this kind of feedback on an announcement post)