Hi,
I found this information on a german coverband website, with some details of NS3 release at Namm 2015:
http://www.lecker-nudelsalat.de/nord-stage-3-2015/
I´m not shure if this is correct, or if they do this to generate more klicks

This is the original text, translated via google:
"After the Nord Stage EX the Nord Stage 2 came and now it will be so far back in December, then Clavia will announce that at the Namm Show 2015,
the Nord Stage 3 for the first time presented to the public. I can not and should not tell the source from which I got this information, I would jeopardize the work of a friend here.
I assure you, however, they are more than hot!
Most essential distinguishing feature, the Nord Stage 3 now has 3 slots.
However, this significant difference suggests to book with almost 700 Euro price list and thus beyond the Clavia 4Tausender brand.
Well, that makes Yamaha keyboards with plastic too, but for Clavia a mighty step up. The other new features are also more than useful, but this is the biggest differentiator.
Furthermore, samples can now be accessed via the piano section.Thus, it is the Nord Stage 3 possible to play on the piano section, a sample and the Synthsektion this to inferior example with a pad without using another slot for it.
Continue to be controlled by another button, the share for each instrument. But the fact remains, a Hall for everything.
Also, the compressor remains unchanged. Not quite sure is the information that sounds can be assigned to a certain velocity range now.
Some small additional changes there will be, but are not quite as much. The drawbars for the organ section, there is then, for example, in the Nord Stage.
As the new street price will look like is not yet known. The list price of the Nord Stage 3 with 88s keyboard should then from March 2015 - earliest delivery date - are Euro - in 4150.
He probably ends up in the store then for 3950, - Euro. Sounds like a lot, but is everything a keyboardist needs. As for the '73, it could be that this is no longer offered but version 3. Final decision but this is not."
Let´s see.......