It doesn't make any BUSINESS sense to release a new iPAD in the same year they release iPAD2.
Apple is still a company in for profit and they have please and answer to their stock holders and investors too.
With iPAD2 sales being really strong right now, and getting very little competition from other players, what business sense does it make for them to release new technology that early?
In that light, Apple should always be investing in R&D and having the 2 or 3 generations of software/hardware and multiple prototypes always in the works so they always have competitive edge or an 'ace' up their sleeves incase their competition pulls something off.
Even if they have multiple working prototypes for the next iPAD/iPhone/iPOD ready they wouldn't release it until it makes business sense to.
Release new products for the sake of release it; will only drive a company out of business.
That said, if Motorola, HP, HTC, Samsum, Asus, etc pulls out a miracle tablet tomorrow, Apple will probably have something already up their sleeves to respond if they have too; until then or Sales of iPAD2 takes a significant drop; you're not going to see a new iPAD until March 2012 at the earliest.