so far, shine JC really does not match fox and his playstyle at all. The pushback from the shine makes it impossible (i think) to get a JC dair or nair, and since there is no wavedash, JC out of a shine will not make you get to the opponent faster than letting shine cancel on it's own. Also, you need to wait for the full dash to complete before u can perform a down-b move (just like crouch canceling), and on top of that all of fox's momentum dies when u shine. I am not posotive, but it feels limited to how fast the JC comes out, bit sluggish i think it is in Fox's jump delay/animation.
Personally, i thought Fox should have the shine cancel he had in ssb64, landing cancel (jump ->fast shine ->land cancels all lag). It really fit his style since foxes that did shine usually jumped before. But i am a huge fan of JC shine and maybe witha few tweaks it will be more useful