This has been discussed in many a thread - Pioneer are doing something in Italy in May. Common opinion is this is the launch of the 8G panels.
I would imagine dealers will have limited stocks through June, and July will be when there's plenty available to all.
Given the Panasonic 50PZ700 Full HD panel is due May too, I can't see Pioneer really dragging their heels over being in the mix with the regular 508, and maybe the 508 Full HD at the same time.
Certainly going to be interesting to see how things shape up over the summer months.