Yes, we have plans to offer such modules and we plan to start working on them in the next 6 months. They will probably be available separately, i.e. they will not come with Sitefinity
by default, but rather will be separate downloads. The idea is to offer modules provided not only by us, but by our customers as well.
At this time we do not have an exact list of modules we will provide, but a Forum module will be one of the first to be offered. We will very much appreciate the community's feedback on what types of modules are most needed.
As to 3rd party products, you can use anyone you like, as far as it is implemented as a control (ascx).