I beleive the WII SD card memory problems lay with the fact that SD cards in order to maximise space do not have registries built into the chips themselves, unlike say RAM chips for a PC computer.
Thus the registries are built into the system instead so it is up to the system maker to increase the cost of the ports in order to be able to utilise increasing amounts of memory in SD cards.
thus the 2 solutions would be either to
A: introduce SD cards that have registries built into them (considering those crazily small Micro SD cards are aproaching 4GB, maximizing space for SD cards might not be sucha pertinent problem as it was during its initial inception)
or
B: come out with a USB SD card reader that has expanded the amount of registers for up to 64 GB 256 GB*crosses fingers*
Never the less on to the main topic this I think may be a neccessity as my hypothesis for the upcoming upgrade will be:
The SD channel
Which will require users to leave a signifigant amount of WII memory card space free, possibly the majority of the space if not all and have everything that was on the WII uploaded to SD.
This free space is of course a virtual memeory to download whatever game or program is selected in the SD channel and possibly to be used to help performace of say, the Web browser and WII ware games.
That is my hypothesis at any rate.