Trolltech has already published two technology previews of Qt 4, and it could be added to Portage tree, to try it and add feedback to Trolltech.
Steps to Reproduce:
I worked on this for some time, but the build system is very incomplete for actually doing an install. Once the first beta comes out, I'll be on top of it.
Beta 1 is out.
I'm working on the ebuild, but it's a bit tricky. Look for it as soon as I can get it to work.