I have looked into the Mario Kart 8 network protocol (which is almost identical to Splatoon, btw.) and it is completely different to MKWii. No surprise, since MKW online was made by Gamespy and the Nintendo Network was made by Nintendo.

The peer-to-peer data looks logical (no encryption / compression / etc) but has variable-length packets (very difficult to interpret).
Parts of the server communication uses SSL, but it looks like Nintendo is using standard curl libraries to do that, so I'll try editing the URL to a HTTP one (like we did for MKW) to see what it transmits. Other parts are unencrypted clear binary data blobs, but some are obfuscated / encrypted / hidden / whatever.

So Wiimmfi itself will definitely never support WiiU games as the WiiU online mode is completely different. I plan on looking a bit into its network protocol, but with very low priority and I can't promise anything.

Also, I doubt they'll shut down MK8 online anytime soon.

Um... I think you're just being overly paranoid about it.

If Nintendo actually owned WFC, it would probably still be up and running today.

Who said it had to use different servers? Why would they go through the effort to make an entirely new server when they already have a perfectly fine one right now?

That being said, I'm glad someone at least took a look at how the login system works for Wii U games.

Nintendo's servers are all integrated into one: The Wii U and 3DS use the exact same server with subdomains. The N3DS/O3DS are also tied into it.
Nintendo will very most likely be adding the Switch into the behemoth of the network, and then if they do shut off the old network, we can setup new ones, but I know private work is occuring on documenting the entire network.