I looked at it this way:

The progress and stuff accomplished in P4 will be saved and carried over. All being there are no need for rollbacks/resets.
(There is no mention of Data wipe in the timeline/roadmap like with other phases)
After BETA they will probably bring the servers down for maybe 2-ish weeks to finalise things.
Early access maybe means instead of 2-ish weeks, us addicts only need to go without our fix for 1 or 1.5weeks, maybe?!

Thats all guess work of course but thats how I personally thought/hope it might work