From a hardware perspective, better hardware power. Any monkey could get games like Mass Effect or Crackdown to work with a wiimote. The reason why they didn't bother with it was because the Wii's hardware was vastly inferior. I wouldn't think remapping control input would be that much of a task.
Also, Nintendo needs to shake the kiddy stigma, and fast. Towards the end, pretty much the only people who bothered with the Wii were the casuals, exactly not the market to build a base on. There's still Wii owners who don't know what this newfangled "U Adapter" does. Yes, there were lots of M-rated titles for the Wii, but none of them sold well. What Nintendo needs is another Eternal Darkness. No, not Shadow of the Eternals, but a mature-targeted title made from within Nintendo. Not from a "come and go" studio like Rare or SK was, but one that pretty much is Nintendo, like HAL or even Retro. Now I'm not saying they should take Mario and turn it into GRIMDARK like Dark Knight Returns did to Batman, but a whole new IP geared towards older audiences.
If the EA snub and almost nonexistant big game release schedule is anything to go by, Nintendo's pandering to the casuals is seriously starting to hurt them