I'm planning/hoping to keep mine for at least 5-7 years.
When I bought mine, I told myself that I'd keep it for 5-7 years, that's why I bought it new and to my spec.
However, I would say that in the next 3-5 I'll do one of the following:
a. Modify the GTI to Revo Stage 2, Militek, Carbonio + my pending Bi-xenon upgrade which I rue not sorting out at factory order.
b. Buy a Golf R Mk2 or 3 potentially if I can tolerate the seats (not a leather fan) and they get rid of that horrid plastic backing that looks ex Focus ST parts bin.
c. New shape Audi A3 (S3 or RS3 variant, probably the latter) but it would depend on how well it stacked up to the Golf R.