Nah, i think it will be alright. AFAIK several people managed to fit 20's on Gen. 1.
As you might know the platform is shared with several GM cars, one of them being the Opel Astra K. A lot of companies offer 19's with TUV approval in Germany and without body work required. Springs are also available by the way, that might physically fit the Cruze.
I know it is not a 1 to 1 comparison, but very close and i think we will see 19's soon on the Cruze. My personal rule of thump is always go 1 inch more than the largest factory wheels.
For the looks 19s are for sure the best choice. Although this thread needs more photos. There is nothing more embarrassing and upsetting than buying too small wheels. Then again if it is not drivable you lose again.
I know this is a general discussion and there are opinions that go both ways. But i would like to here some actual experiences with the new Cruze in particular.
I had 18s with 225/40 (which happen to be the RS wheels size) on forged wheels before on similar cars and in terms of potholes etc. it was no problem at all. Never busted one.
19s on the other hand are a different kettle of fish... with 235/35 side wall height is a reduced by .3.