105 Di2 - is that coming? And what about 12-speed GRX Di2? And MTB?

Yes, the answer is yes to all of the above...

At least, that is my best estimate. Shimano are definitely working on Di2 versions of 105, and updates to both the GRX and MTB Di2 groupsets.

As for when 105 Di2 will be released - it seems to be coming June/July 2022. I'm not sure when you can actually get your hands on the groupset though. Regarding the MTB update and GRX - who knows? It's safe to assume one of these will appear within the year, but I'm just guessing here.