The WiiU checks things about the NFC tag that you can't spoof without specialized hardware. Also, the places on the amiibo that say what character it is aren't writable.
What I am doing is reverse engineering all of the file formats, and using a hacked WiiU to test them to confirm changes.
Most recently, I made
http://opensa.dantarion.com/s4/mastercore3/ showing all known changes in patches.
Now, I am working on getting modified files loading off SD, or over wifi.
Soneek has successfully done over wifi, but because of the internal archive format of S4, its a bit hard to do it the proper way.
The missing piece as far as I am concerned are breakpoints. Without those, I cannot debug things very well, so thats the main focus at the minute.
I want to make more vids, but I want to make vids when I have a completed PoC mod to show, and not just tests of poking aro und.