Open Whisper Systems partners with Google on end-to-end encryption for Allo. https://whispersystems.org/blog/allo/
I get where Moxie is coming from, and that he doesn't have the PR machinery that Facebook and Google do to really push Signal to the mainstream, but these are advertising companies.
When OWS takes this work on they're giving a tacit Moxie stamp of approval to the implementation, that could well change after OWS has moved on to other things.
tldr; History tells me not to trust these companies motives in the long term, and I don't see why Moxie should either.