Funny as it might sound, I have a customer which runs ]po[ and now needs communities for it's users. So we might be installing .LRN on top of ]po[ and write a dotlrn-portlet for the list of projects and tasks of a user.
In your case you could probably just make projects subsite aware in the sense that they know which subsite they belong to (even if the intranet-core package is only mounted once). Maybe just use the parent_id ?
Then you have the control of the projects in the communities.
But, as Frank mentioned, going with project-manger and the dotlrn*project-manager* stuff is probably easier to achieve for your goals.
