I was wondering...

seeings how it's possible to wrap the entire PHPBB3 forums in side Joomla whats stopping you from creating the ability to just wrap a single forum or category inside a module position?

What I was thinking was that if we could run a single forum or category inside a module position we could use PHPBB as the discussions inside the Jomsocial groups.

All you would have to do is link a group to a category and create a PHPBB3 theme that gets rid of the all the board navigation elements so that it kind of locks them into that category or forum. When someone creates a Jomsocial group you can have the integration create a PHPBB3 group and category/forum and link them together.

There is a guy that has this for Kunena but the problem is Kunena does not have the internal groups feature so if you start a private group in Jomsocial other users can navigate into your discussions because there is no permission keeping them out.

This would be awesome and I would be willing to pay $50 to $100 for this type of integration.

This would be useful

Started developing such feature for the bridge JS application.

If the above is possible why is it not possible to link JS and phpbb3 groups?

It is possible, but not now - no such option right now.
But we are working on it.