** If you decide not to update you will be able to use a future homebrew channel for wii u when it comes true (allowing region free, usbloaders, howebrew, etc..) - but I think (not sure) you will not be able to access the e-shop, I don't know if you will be able to play online with mario kart 8 for example...
At the moment the exploit only works on firmware 4.1.0
*** If you update you will have your console up-to-date enjoying all the online features and with the next update nintendo can block the exploit and no one know when/or if, a new exploit will be available, I mean no homebrew, hacks, etc....
WiikeyU is a piece of hardware that seems to be about to be released(?) according to some posts here on gbatemp. It is an ode (optical drive emulator). As in ps3 the Odes can be blocked as sony has just released the firmware 4.60 for ps3 and blockED odes from working (it barely works on ps3 super slim models). So just time will tell if the odes will work on wii u after Big N releases new firmwares updates.
That's your choice to update or not.