Tuning a GDI

I was thinking a bit about what the possibilities would be with tuning an gasoline direct injected engine, like the ecoboost from Ford. In theory, you can achieve amazing results, like huge power but still being fairly economical because a very lean air fuel ratio is possible.
I was wondering what the limits are of tuning a GDI in real life. If you put a bigger turbo on it, would you need to use an aftermarket ecu, and also do ecu’s to control GDI even exist yet? Does anybody have any experienc with tuning a GDI?
I’m thinking about how useful an ecoboost engine would be in a daily drivable sleeper build.
Thanks for any input and sorry for bad English!