Pretty sure we'll have a flashable stock jelly bean rom available as soon as the OTA for JB is released. It's really trivial to package superuser and the su binary with the stock ROM. If the official ROM is leaked early, we'll have the rooted version early as well.
I see no reason not to root or unlock the bootloader in advance. And given that the root method used to root the Infinity is the same as the one for the Prime, I suspect the exploit won't be patched either, but who knows. Safer to root now when you know there's a working exploit. Then just flash a rooted stock ROM. Again, the rooted flashable ROM usually comes as soon as a dev gets a hold of the stock OTA package.
This is one advantage Android has over iDevice jailbreaking: once rooted, you can stay rooted and still get stock updates via flashable rooted stock ROMs. With a jailbreak, you have to lose your jailbreak if you want a newer iOS version; then you have to wait for a new jailbreak exploit.