> they haven't released anything new in two years, after exhausting the backlog of already developed things.

I'm not a Twitter user, so I might miss the lack of some essential features, but it seems to me that the platform is mostly feature-complete. Just further bloating the software for the sake of it is not necessary a good strategy, yet it is one that a lot of startups follow, just because that VC R&D money has to go somewhere.