I'm trying to say, that there is a time period (between 5.1.5 and 5.2) where there is no possibility to upgrade at all. The longer that time period is, the more likely it becomes that upgrades will fail, as we are notorious for broken upgrade scripts. Therefore my suggestion was to wait to cut the last release until the next beta is available, so we can make sure upgrades work and an upgrade path exists.
After all, there is no incentive to move a (not important, production) site to 5.2 if there is no guarantee that you are able to upgrade from that version to which you upgraded to.
Maybe this makes my aim a little bit clearer.
