I wouldn't say KiCad is usable yet. I've made multiple attempts to use it and it just is fundamentally user hostile. Unfortunately the devs see any attempt to improve user friendliness as "dumbing down".
Fortunately there is (finally!) an open source PCB design program that doesn't suck: Horizon EDA. I've only made one PCB with it but honestly it was pretty great and the author fixed every usability bug I reported in a matter of hours, which is an insane difference from KiCad's "you're holding it wrong".
The only think I don't like about it is it has an unnecessarily powerful and confusing component system (there are modules, entities, gates, etc.). But really it is the best by far.
Anyway, on FPGAs, I think the tools are only vaguely mature for iCE40 and even then you basically need to already be an expert unfortunately.
