I think to be reasonable, a Smash game would look reasonable on the Wii in about 4 to 5 years from now. Most people want a sequel on the same console, so looking at how its a competition every decade with new generation consoles, a Smash game would look good in that amount of time. It takes about a year to to two to do a sequel, so yeah, we could start thinking about it during or after 2012.
With a sequel, not a new game at all but a sequel, meaning just additional content and almost invisible tweaks in mechanics, we should see a new SSE storyline, new characters introduced to the fray (with Brawl and the pattern we are assuming thanks to people who noticed it, it seems 15 newcomers are to be expected at the most), a better online system, more items and stages, maybe more Stage Editor parts, a few more games added to the Chronicle and Masterpieces section, and a possible chance of DLC if a Wii external drive is made.