If D3 open beta came out right before SWTOR dropped and it was more fun than SWTOR many people would pass on SWTOR. I think Blizz is keeping beta numbers low because they don't want to steal the WoW 4.3 thunder.
Now if Blizz waits too long to release D3 they will run into the second issue, GW2. If somehow GW2 is more fun than D3 AND has open beta weekends before D3 releases then D3 will be in a ton of trouble.
As for announcement of release date. Either this week to increase Black Friday pre-orders/marketing (unlikely) or around mid-december right after WoW 4.3 drops but before open beta/SWTOR.
Blizz does not care which game you play from them. They are using WoW + D3 to crush SWTOR (smart move). Chances are one of those games will appeal to you and keep you a Blizz customer.