Shimano have just announced 12-speed XT and SLX group sets - and we've ridden them.
The all-new Shimano Deore XT and SLX
The best news is that Shimano Deore XT 12-speed shares just about all the tech from Shimano XTR 12-speed. Here's a run down on the parts.
These are essentially the same as current Hollowtech cranks, but with the direct mount chain ring option. In fact, if you have a set of MT900 cranks (shipped with XTR group sets while the M9100 cranks were delayed) you pretty much have an XT crank with an XTR chain ring.
XT chain rings run from 28-36 and they are a two-piece ring with steel teeth for durability. If you wanted to run a 38t chain ring you could fit an XTR chain ring - they're compatible. Similarly, if you have XTR cranks and want a 28t, you can fit an XT chain ring.
The SLX crank has a raw metal looking finish - but is essentially the same crank with a slightly more basic chain ring. Again those are corss-compatible, but SLX chain rings run 30-34t.
The XT and SLX crank sets come in 3 Q factors for 3 chain lines, basically for non-Boost frames, Boost frames and super Boost.
Shimano have kept a 2x crank set on as well, with a 26/36 ratio. It is the same crank but the big ring direct mounts to the crank and the little ring attaches to the big ring.