I haven't done it yet and wondering if I will. I am blown away by the SQ of the G2 (and to think just a few weeks ago I was in the "all streamers sound the same" camp...) But I do find it kind of glitchy in a way that makes me not want to mess with it too much when it's running fine. And my local files are not such a huge part of my listening life, so having them attached via USB drive (which works just fine) is not that big a deal. About the only thing I think I would gain is that it would be easier to add files to an internally mounted SSD but the truth is I don''t do this that often.
This all may be a way of me saying that I am lazy and have other things I'd rather do than this. Also I tried to put an SSD in an old mac mini a few years ago and despite doing everything right and the mini recognizing the drive for some reason I could never get an OS loaded onto it again and just gave up. That memory is informing my reluctance - I really don't need that type of inexplicable mess with the G2 right now.