This was a bad choice of a WiiU game to port to the 3DS anyway. A slower, less demanding game would have been the perfect choice.
I agree that midterm updates are bad in general, but it would hurt Sony even more that it does to Nintendo. The N3DS just has one must-buy game (which is accesible on both Wii-WiiU) and a SNES emulator. Is Sony makes a more powerful PS4 version, some of those 3rd parties would consider moving their projects to the upgraded version, and considering Sony machines get a lot more software, the amount of content unaccessible (or bad performing) content for the +40m users of the original model is going to be big. And no company wants to piss off 40million of their customers.