10 speed, I presume you could upgrade to at a later date, so no worries, but if you just built a bike from scratch with all new parts, maybe you should have seen that coming, the writing was on the wall many months ago, if it bothers you that much?. The Syntace 142mm (X-12) rear is no great step forward really, just a bit easier to slot the rear wheel in over 135mm. It’s still in it’s infancy yet and may die a death. Trek use it as do Cube (for a few years now), but it may not take off as a popular standard. If you’re worried about 142mm rear becoming the norm, just make sure you have/buy wheels/hubs that will adapt to it at a later date ie Hope pro2.
The days of being able to buy a new frame and just bolt all your old bits to it without extra cost and faff, seem to be gone.