Hmm I don't see the point to be honest. Fixing bugs is not something we reserve for a particular release and the rest of the time we keep bugs around, it's something we work on all the time on all versions. The software being reliable is always a top priority.
Although if you're asking for this perhaps it's because your favourite bug is not being fixed, but having dedicated versions won't solve this. Sometimes we don't have the resources, or just don't know how to fix a particular bug. Or it would take way too much time to fix it compared to the impact it has. It's all about prioritising.
Just a question. A bug related with the actual version 1.8.x could be fixed in both versions (1.8.x and beta version 2.0.x) at the same time without adding you to much work (test…) ?
We backport regressions or critical bugs, but otherwise we expect users to upgrade to newer versions, because maintaining long term older versions is not practical.