For me there are 2 big issues.
1. Power. The fact that the wii U isn't getting current gen games isn't the end of the world, but if the system isn't powerful enough for developers to comfortably port ps4/720 games then that will be a problem.
2. Developers are stupid. "Mature games don't sell on nintendo platforms!" I've seen many imply...
Oh, really... and they gathered this from masterpieces like Dead Space extraction underperforming. Or what about the other mediocre titles that people use as evidence like Madworld, No more heroes, conduite...
All the evidence you need is that resident evil 4 sold 2mil on the wii even though it is a port and was released whilst the wii's userbase was under 12m. Like any platform, the nintedno userbase is going to respond to a combination of quality and accessibility. So until developers bring forth a commercially viable title with the reviews to back it up, then they have no evidence that mature titles don't sell on nintendo platforms. Nintendo could go out of their way to try and prove this by partially funding a nintendo exclusive mature title with all the makings of a AAA smash hit.
I believe they tried this with DS and GTA but even in 2011, a top down GTA might as well not be GTA. Not to say that China town wars wasn't good, it just isn't what the majority of modern GTA fans are looking for. If there was a vice city story-esque game built from the ground up on the 3DS, I'm it would see similar sales to the psp iterations (2-3m)