Honestly, I doubt ps4/xbox one multi platform games could be 'faithfully' ported to the ps3 and xbox 360.
Here's an excerpt from an interview with a dev from Witcher 3:
"How was development on next-gen consoles for you? How much of your vision did you have to sacrifice to gain stable frame rates on the PS4 and Xbox one?
It is extremely manageable. There is a lot of power in these machines, and I don't want to say we're using them to their capacity, but we're fairly close to doing so. We made a decision to go next-gen roughly two and a half years ago, so we've spent a lot of time with these machines, and it's been a great experience across all three platforms. On the old platforms, namely the Xbox 360 and PS3, we probably would have had to sacrifice nearly half of our vision."
If they had to sacrifice roughly 50% of their vision to get Witcher 3 on the xbox 360 and ps3, then it would practically be an entirely different game. Based on the above quote, I don't think next gen games (i.e., ps4 /xbox one) would be able to be ported to current gen platforms, including the wii u.
full interview here: http://au.ign.com/articles/2014/01/23/the-witcher-3-new-details-to-blow-your-mind