Bahh. I accidentally clicked the “Post” button before I finished. Anyways...
When that’s done your Wii will be back exactly as it was when you made the backup with all your games and all your saves just as before. The only thing you won’t be able to use is the Wii Shop Channel. If you do it will remove all the games that made the transfer to your Wii U because the Nintendo servers check the games when you connect.
Since the Wii Shop Channel is dead anyways this shouldn’t cause you any issues anymore as long as you make sure to DL everything still available BEFORE doing the NAND backup. So make sure to redownload all your games and the Skyward Sword Save Fix so you’ll always have it otherwise you’ll have to use different means to get it later on.
If you do accidentally click on Wii Shop you can always do another NAND restore. To avoid all this it is possible to remove Wii Shop altogether using Homebrew. I haven’t done that yet myself so I can’t help with that one but it’s probably worth doing now that you’ll never need it again anyways.
Hopefully the System Transfer Tool remains available into the future because the other thing about Wii to Wii U transfers most people don’t know is you can transfer multiple Wii’s to one Wii U. So if you find a Wii for cheap with a bunch of digital games still on it you can transfer them to your Wii U and they’ll combine with your games that are already there. I got one for $5 that doesn’t read discs but it had a bunch of Virtual Console games that are now on my Wii U along with the ones I bought on my own Wii.
I hope this helps anyone who like me never did the transfer or maybe people who get their first Wii U in the future and are interested in moving their Wii stuff to it.