I haven’t seen any development addons for Domino Designer that could make it more social.
It would be great to have some integration that you easy could update what design elements or/and databases you are working with.
Also a easy way to update status in your projects.
I would be happy if you could have integration points in the designer that don’t require the use of creating a plugin.
Perhaps a side panel that can load an xpage and some scoped variables gives integration with the designer.
Java UI API support from XPages in the client wouldn’t be bad either.
You can integrate it with Rational Team Concert 2.0. That has social features