Version 4.0 is a beta version, more or less corresponding to version 3.3, except for the internationalization features. I never tried it but I'd say you can run version 3.3 MODs with 4.0. Obviously the language will not be as easily changed as with 4.0. If you try to use the MODs with 4.0 and if you customize it for 4.0, it would probably be interesting if you did it following the rules for 4.0 compatible MODs...
What? The active users and private message mods? If that is your question, no I don't. As far as I know people are not developing MODs for 4.0 because is still a beta version, it's code is not finalized. The final version will be quite different from what it is now. It will be changed to take into account all the changes for version 3.4 (expected to be out any time now) and probably more.
As I told you, it's likely that you can use most (if not all) of the version 3.3 MODs with version 4.0. Why don't you try it?