It would bei cool if there was a posibilitily to chose how to sync Pictures an Videos separatly I would like to sync Pictures on both WIFI and 3G but Videos just on WIFI with the App
I assume you mean the Android app?
To me, this sounds overly complicated. Maybe it could be done with the proposed Tasker integration.
If syncthing will get the functionality to pause/resume single folders, you could implement a per folder setting for sync on mobile, sync on wifi and perhaps sync on specific wifi (which is one of the use cases for the requested tasker integration).