Well, enabling it (for Win32 anyways) is only 10 lines of code, so it's hardly clutter.
As Laurent pointed out: API clutter, not code clutter
Still I don't think that native GUI integration needs to be a basal feature. Look at other, similar frameworks like SDL or Cinder: They also don't have any native GUI integration.
If you are unsure: Start a poll to gather the opinions of the community.
The main advantage of SFML imho is that only needed features are implemented. However, if the majority wants that integration Laurent shouldn't be hesitant either
