Although it seems obvious, I guess it bares mentioning. SE is intending to support DQX for ten years. Not necessarily the Wii version of DQX though. That's support will end when enough people have switched to the WiiU version instead.
Once the Wii numbers are small enough, it'd even be worthwhile for them to offer a trade-up special. Trade in the Wii version for a cheap/free WiiU version (they'll make the $ back off monthly fee and off savings from shutting down Wii servers/updates).
Since no-one (not even port happy NoE!) has announced DQX for Wii we can assume only a WiiU version will be available outside Japan (if at all).