The V-6 contraint was there because there were more V-8's sold than were expected, so they wanted to get the ball rolling by only producting V-8's at the onset. (at least that is the way I understand it)
My guess interpretation...
It has been stated that production is set to be 50/50 v6 vs v8 (I don't know if this is office, just what I have heard). Initially, the v6's they were making are for the dealer show cars for the may 6th launch. It has come off restraint now because those dealer cars have probably already been slotted for production, so going forward, they can start to work on pre-sold v6's.
Since the pre-sold was something like 90% v8, it is rumored that if you order a v6, you may get it sooner.