I too am interested in the roadmap for the Version 7 release.
It says Alpha... Presumably it still has to go into Beta for sometime before being considered stable?
I'm wondering if I can get away with installing it and patching it as updates come out, without losing the system...
First off, do not run the 7alpha version on a production server.
Also, updates may or may not work correctly. 7alpha has moved from centos3 to centos4.1 midstream (alpha22 or 23 if I remember correctly). Updating did not work very well. Some alphas had major package changes and thus the reason it is still alpha. The next alpha appears to even have some directory structure changes.
When it reaches Beta, it should be much closer to the final version. Patching/updating from beta to final will probably be a better idea.
The developers are going at it in a feverish pace. 20+ alphas in just over 3 months, that's almost 2 per week average.
When will it be ready you ask? The standard answer applies here: "When it is ready!"