The 2017 may be a better option for you then if you're really concerned about future things. I'd say in 3-4 years 10bit will be more of a thing, but which time you'll probably be upgrading anyway?
Otherwise the 10bit side of KL largely affects battery consumption. Both are capable of encoding/decoding, there's some question over the efficiency of playback but everything I've seen relates to 4K 10Bit 60Hz.
Which A7? A7S is h.264, A7SII does h.264 too. Obviously standard A7 is a stills camera capable of 1080p. Could be wrong, have they had a patch to enable h.265?
Anyway, if cost is a concern. Why not just get a 2016 and see if it works for you? If you could wait for High Sierra you'll be best off but you could probably make a fair assumption based on the Beta.