Just my point of view:
.Net Application server: Definitely Yes! I start to look at JBOSS. I think that we should migrate it to .Net. Migrate and not convert because we can use .NET (attributes, codedom/emit, generics, generic aware reflection and app domain) to create more faster and robust solution then JBOSS. But I think that JBOSS is good starting point, eventually several PhD's came out from that project and jboss already prove himself.

I don't think that Microsoft should do it alone. I think that MS with .Net community should do this immigration as open source initiative so both Microsoft and the community can gain benefits.

I don't think that Microsoft doesn't try to get a position in enterprise development. MS try to do it by investing in community, developers and so to penetrate enterprises from low level. Well, that might work (I'm not marketing genius Smiley ) but without competitive tools to other vendors in the market I really don't see MS as leading force in enterprise development.