If you want to exploit your Wii U, DO NOT UPDATE TO 5.4.0!
We shouldn't be needing to remind everyone about this again, as far as I remember we told everyone that a new update (it was either 5.3.4 or 5.4.0) would be out in a few months and that you should block updates on your unit.
It's impressive how after so much time working on this and finally getting there yesterday, Nintendo figured out exactly what bug it was and patched it not even 24 hours after. Yes, Nintendo simply updated from 536.28 to 536.30, just enough to patch the bug we are using (go figure which one it is from the ChangeLogs).
At the same time, it doesn't really surprised me, Sony did exactly the same with the 3.3x bug by updating their WebKit source code from 537.73 to 537.73.2 before it was even released.