Let's assume, momentarily, that in 2011 when the VC release schedule dried up, it was due to a combination of prepping 3DS titles for VC and the knowledge of a new console on the horizon from Nintendo. By the time the Gamepad and features of it got pinned down and finalized, it would have been 2012. Work on migrating them over and working on new releases for VC to support couldn't have even started until then. 600 titles changed over in less than a year? Yeah, I don't see that happening. Considering the Wii's VC library, they'd need a good chunk of them ready to go before they re-introduced them, as many of us remember things like the 360 backwards compatibility scenario, where gamers were asked to wait and wonder when the stuff they bought would be compatible. Better to have a large amount ready at launch and fill in the blanks later.
And let's not forget potential legal hoops involved if Nintendo wanted to, say, allow VC purchases to work on more than one device per purchase.
There's a lot of factors involved, so until we see an end result, we don't know what's keeping them from being released.