I tried this hack with Dolphin Browser beta. I couldn't get it to recompile.
Regarding gmail. It's a downloadable app in the play store, yes? Just like youtube?
It's a system app on this phone, but with root we should be able to replace it. If it doesn't work, simply put it back.
I know on my Nexus I was running a custom ROM. I wanted the new gmail app, so I deleted the one that I installed on the ROM with the one from the play store.
EDIT: I just saw that there is an update fixing the recompile problem. Now I see what you guys mean with the 1.apk