Mmm. The Mk5 was certainly a big change. The 6 obviously wasn't, although was a subtle evolution of the marque. The 7 will probably follow this trend.
The saying 'fashion fades, style remains' I think is very relevant to the Golf. Supposing they went mad and radical - I wonder would they alienate a lot of their market? I think they'd actually make the car more desirable!
Thing is the Golf is a good looking car, so maybe there's no point in really changing a winning formula that's been a success for 35ish years.