F*ck yeah, it's a great thing.
Lots of people missed out on the handful of great titles that appeared on the Wii U. Bringing them over to Switch gives developers a chance to sell their game to a whole new audience, and it gives a whole new audience a chance to enjoy those games. Many of them sort of languished in obscurity on the Wii U.
It also helps Switch build up its library of quality exclusives quickly. Switch is off to a strong start in terms of game announcements, but this helps to build that library even faster. Porting is a lot easier than developing a game from scratch, of course, so they can get them out there rapidly. Nintendo is ensuring that these will not be straight ports, either, and that there will be significant improvements for each.
I was considering a Switch for Zelda and Mario Kart 8 (a Wii U port). The new Mario looks fun, too. But only 3 games is a little thin, to justify a console purchase for me, especially when I know it'll only be used for exclusives, not multiplats. But if they brought over Bayonetta 1 and 2, Xenoblade Chronicles X, and another game like Wind Waker HD or Donkey Kong, then I'd be looking at 6 or 7 games I like to play, rather than just a few.
Adding 3 or 4 enhanced versions of great Wii U titles would probably get me to buy a Switch. I'm guessing I'm not alone. It's a great way to bolster its library of quality exclusives.