Today, Mark Pryce-Maher left a comment on my post reporting the lack of support for SSMS extensibility in Denali.
Mark just started a series of posts on how to build extensions for Management Studio in Denali by leveraging the isolated shell it is built on.
Basically, you can build Visual Studio extensions and then targeting the isolated shell of Management Studio, making it a little bit easier to write add ins now than it was in the past.
You can read Mark first post on the topic here.
Update 1 : Mark has published the part 2 of his article here.