As usual, M$ does a little too little, a little too late. they should open source their entire codebase and maybe then it will make up for the damage they inflicted with their schemes to lock in vendors, developers and users alike with their dirty, exclusive practices for decades...
I highly doubt there is a shred of noble aspiration behind that decision. M$ either sees a drop in developer base, prompting it to pretend to be nicer, or more likely - opportunities to entrench developers who would normally not touch their development tools.
If their .net APIs are as ugly as their RT C++ APIs, I would not worry about Qt losing relevance to a portable .net. And somehow I have my doubts M$ will ever invest effort into supporting nice high level features on competing platforms.