The WiiU will have an SDHC slot; not sure if it supports SDX
C yet, but the system has yet to come out... and it could be like the Wii that initially didn't support SDHC cards, but was able to after the 4.0 System Menu update.
Launch games for the WiiU would only support one touch-screen controller anyway... though it has been stated that they intend on bringing support for at least two per system down the line. And as Silvanos
pointed out, the WiiU will natively support existing Wii remotes, et al, as it's directly BC with the standard Wii.
Further, unlike the current difference between standard and modified Wii's, the WiiU will natively support external storage this time... I think Nintendo learned its lesson form the hacking community on that one.
Because, f*ck Sony