Hi Sean,
One of your readers said MH3U for Wii U was a sequel. It’s not. It’s an HD port of MH 3G which itself was an enhanced 3DS version of MH3 Wii. Capcom has historically done “G” versions of previous MH games with more content. Those versions would usually appear on the same system as the original release, but 3G was an exception, going from Wii to 3DS, and now Wii U. Picture MH3 Wii, only in HD with more content (how much, I have no idea) such as new monsters, local co-op and 3DS <-> Wii U co-op on top of the online mode which was already present on MH3 Wii.
The actual Monster Hunter 4 has already been announced for 3DS, though details are scarce.
All the same, if I get a Wii U down the line, I too am glad I never bought MH3 (almost did!).
This is what I thought. I thought Monster Hunter 3 Wii U was another update of an update to Monster Hunter 3 (hence the 3 in the title). The sequel is Monster Hunter 4.