I have a feeling this will be the Nexus Two (or whatever) with HTC branding on the front. The Nexus S is known everywhere as the Samsung Nexus S, so it could be a logical extension of the manufacturers branding.
It seems to make sense that the next Nexus phone would have a qHD screen, dual core CPU and be a 4.3" device, after all this is where lots of phones are going and the Nexus line is meant to offer some sort of reference design.
After the Nexus S, which I am now selling so I can keep my Desire HD, I would welcome a Nexus phone from HTC again.
As for the OS, I wouldn't be surprised if there was an Android Honeycomb for phones version (which could be a 3.x or 2.4 or something else) and this device launches that version. I cant help but remember that the HTC Passion name was rumoured for months before the Nexus One came out, this device may not be out for months yet....
On the other hand, this could be all be fake. Or the Desire HDS or something...
I would list my devices along with current device here, but it changes too often.