[new] RN12T1230 (36TB)

Well assuming such a product is coming I expect it would probably be very similar to the existing 4200 models. Until/Unless NetGear officially announces such a product they likely won't comment on it.

One can make some guesses:
Dual PSU - Can't see why it wouldn't have this. Dual hot-swappable PSUs is a key high-availability feature of he 4200.
10 Gbit slots - It'll probably have the same optional dual-NIC 10Gbit PCIe options
Which hard drives? - Enterprise 7200 rpm hard drives, of course. Reliability and performance are key. Most likely disks on the compatibility list for the 3100.
Throughput - should be at least as good as current 4200. I don't know whether or not NetGear would use the same CPU.
which controller - one that supports 3TB drives, is fast and reliable.

This product is listed on the NetGear website: http://www.netgear.com/business/products/storage/readyNAS-4200/RN12T1230.aspx

So the 4200v2 appears to be a silent update to NetGear's line.

Hm, but still no specification sheet on thie new one. Unfortunately it is not SAS based with dual controllers...

I believe the 8 port controller on the 4200v1 is SAS/SATA but only SATA disks are supported. I expect the same would be true on the new 4200v2.