I was asked this question, and I think that the answer is interesting enough to post here.
There are two sets of technologies that MS is currently pushing.
There is Linq, which is additional support for querying directly from the language, and there is the various ORM efforts that Microsoft is pushing.
When the Linq bits will stabilize to the point where it is viable to start projects using them, there will be support for querying NHibernate with Linq.
I have looked in detailed into the four (or is it five now?) ORM efforts that microsoft is currently pushing, and I am not seeing anything that excites me there.
Early feedback that I got from Microsoft confirmed that even ADO.Net for Entities, which is the only ORM effort that tries to match NHibernate's capabilities, is not going to be extensible enough to support what I and my customers needs. This is the usual 80% solution, with a hood welded shut in all the interesting locations.
In addition to this, I find the whole configuration schema to be an order of magnitude more complex than it needs to be, with the additional complexity that this would bring later on when trying to understand what it means.
So no, I do not believe that Microsoft pushing their ORM efforts would have a bad affect on NHibernate, and having Linq would just make our life that much easier.
That said, an ORM that comes from Microsoft is probably going to be popular because it comes from Microsoft. I believe that this will merely confirm for many in the .NET world that ORM is a valid way to work.
The same people that are currently using or evaluating NHibernate will keep it, those that would never use a non Microsoft tool would use the MS ORM. Not that much different from now. People trying to migrate all but the simple projects from NHibernate to MS' ORM would run into the afore-mentioned brick walls, and would either keep using NHibernate, or would have to invest significant effort porting the application.