There’s both kernel and browser exploits found on Wii U up to the latest version.
both browser and kernel exploits are released for 5.3.2, and the same kernel exploit works on 5.4.0 except that the browser exploit for 5.4.0 isn’t yet publicly released.
In my opinion there’s enough ground for developers to make/port homebrew/emulators etc… And that would definitely attract more people to the scene and make it more successful, I bought the wii U first time last year when MK8 came out, but then sold it few months later. But the hacking scene has encouraged me to buy it again. Now I am on 5.4.0, and I’m hoping there will be some homebrew work done already so when the exploit for 5.4.0 is released I would have more interesting things to do with my Wii U.
The firmware version should not be our concern, since we might figure out later on how to spoof/emunand or even downgrade.
I find it unfortunate to let go such a powerful console with such potential without good use.