I don't know if any of the RCs will be encoded. Last I heard - they wouldn't be.
We have not promised an upgrade path from betas to RCs, and in fact have quite frequently stated it is very likely there *won't* be such an upgrade path. It is extremely likely that when RC1 is available, it will only allow you to upgrade from 2.3.6 or lower to RC1, and not from any 3.0 betas to RC1. We don't know for sure yet, but there have been many upgrader/installer bugs that as they get fixed can't be retroactive.
Do not plan to use a beta and upgrade to an RC release. It may or may not be possible.