I'm quite optimistic about a usable Linux phone in the near future, maybe 5 years from now or so. When smartphones were a new thing, it was really hard for open source projects without a major company backing them to keep up with all the new developments. Hence all the projects that died out. But innovation on smartphones has basically come to a halt these days. Sure, your phone can get a little bit faster and have round displays now, but nobody cares anymore. Nothing of all that is essential. So, give it some time, we'll get there.