The news drought coming from Nintendo forces us to speculate, so I'll make a new NX thread per day until we get some official news from them.
I think the NX will be backwards compatible, either by having physical BC or digital only BC like the XBone. However, there's the posibility that the NX won't play WiiU games, specially if we think about the handhels part of the system. If that were the case, I think Nintendo would remaster most of their WiiU titles. After all, some of them are very expensive titles, and they still have a ton of potential sales-wise.
In case of the NX not being BC,how many WiiU games will be remade for the NX? Which games would be remastered? I think at least six games would be remastered: Xenoblade X, Pikmin 3, both Bayoneta 1 and 2, The W101, Smash Bros U (instead of taking two or three years making a new smash, just have the old one updated with all the DLC) and DK Tropical Freeze.
What about Zelda U? I think they will run the same on both WiiU and NX, and both versions are being made at the same time, so it doesn't count as a remaster. Also, we have yet to see how the handheld part and the HC interact with each other before asking for Mario Maker.