I've been using /e/ as my primary smartphone for a couple months now. It's certainly usable: The experience is more pleasant and integrated than stock LineageOS + MicroG, but there's still quite a few rough edges.

I hope they can make a go of it, but I think it'll take adoption by a deep-pocketed sponsor (Samsung? Huawei? The German government?) before it would be polished enough to be a real contender for non-technical users.

But I do think the idea of an Android fork that maintains some compatibility with existing apps is more likely to find success than something like Sailfish OS, that's entirely distinct.