If you always install to USB and not NAND, and you're sure you're not installing a system title, then the risk of bricking should not be very high at all. At worst Wii U fails to boot with HDD attached, just unplug it..I was just thinking about the posibility of using edited tickets files and a whitelist removed Wup Installer, that way you don't really need IOSU access but the risk of bricking your console would be high.
Of course this depends on the nature of the exploit which we have yet to see