I had built modularized Qt5 packages (except qtdocs and qtwebkit) for Archlinux x86_64 a few days ago, but unfortunately I did not have time to write even a short blog post for the time. Here you can find the packages:
There are python3 issues with WebKit for now, so it is not included. I had submitted a patch, but I have not yet had time to continue the investigation. As it turns out the issue is more complex than previously thought.
Nevertheless, It should be fixable by using python2 if someone is interested in that.
I will try to keep it up to date once 5.0.1 is out. Hope, it helps.