The only concern I'd have with Sony APSC is that Sony themselves already said their focus is on FF. So going forward, you are not going to find many new APSC lenses and the existing ones aren't that great imo. That means eventually you probably will end up having to buy FF lenses for the APSC body which are more expensive and larger/heavier. Just another food for thought.
I get the feeling that they are interested in the A6300 primarily for video (haven't looked too far into the back posts), in which case they are going to want manual lenses, of which vintage primes will be adequate. That, and Samyang lenses. All of Sony's lenses are focus by wire, which won't work with follow focus equipment. That, and mirrorless cameras are godlike for manual focus.
I'm away from my lenses/camera now and I can't recall them all off the top of my head but it's a decent collection of lenses, not stuff I'd necessarily want to move on from just for the hell of it. My reason for upgrading is that I'm moving away for a while and I want to get a new camera before then. Most of my photography is nature/wildlife but I expect I'll be doing more urban photography in the future. As it is now I'm almost certain I'll end up giving up on the FX dream and just go with the 500.
If you've already got a system built up, I wouldn't switch unless there's an adapter, or if the switch comes with a great benefit.
For example, if ALL of your lenses are APSC only, then you'd need to get full frame lenses regardless of which company you choose, so there isn't much ecosystem barrier to that.
Keep in mind lens compatibility and what you can get out of it, might help save some cash -- ie Nikons can use ANY lenses made all the way back to their film cameras, so you can pick up cheaper vintage lenses to save some dough, whereas Canon EOS system cameras can't use FD lenses. Likewise, Sony E mount systems can use *literally any* D/SLR lens pretty much ever, as well as I think most if not all rangefinder lenses, given proper adapters. I mean shit, I literally don't have a single Sony lens for my A7II ("But there's no lenses! Bullshit ahahaha)
EDIT: Just remembered, Pentax K mount is the same way. I hate to forget a company, even if they aren't as big as they used to be (but seem to be making a push back into the market).