I'm not sure what the benefit of having some of the plugins being official eclipse projects would be. Also, i don't have any knowledge of the process/requirements of the proposal rules.
I think we should take a pragmatic approach and first plan/design the functionality which will build the "base" PDT-Extension API/framework. If later on it turns out that the quality
of the core plugins is meeting eclipse foundation standards, we can still think of making an official proposal where it makes sense.
One of the main problems i see here that most of the PDT extenders work on plugins in their spare time and therefore might run out of resources eventually. That's why there's so many abondoned projects
out there (e.g. the formatter from the japanese developer).
If we manage to create a lively community around PDT and the available extensions, we might keep those projects alive even if the original maintainer quits the project.
So probably the most realistic and straight forward way for the eclipse foundation to help the PDT-extension efforts is by hosting the central extension p2 repo / mirror.
I have prepared a project where you can test the idea: https://github.com/pulse00/p2-mirror
Running mvn install && mvn site will publish the mirrored p2 repository to http://pulse00.github.com/p2-mirror/