I expected 4M worldwide sold first week (since launch until first sunday) and around 8'5M worldwide at the end of the year so this seems to be on track. Smash is not that popular in Europe as in North America and Japan, but I expect huge sales in USA. For the first week, something like 2'0M US, 700k Europe, 900 JP and around 400k (maybe a little less) in the rest of the world.
Probably will be the biggest launch for an exclusive game ever, but I think Smash will be a lot more frontloaded than Mario, Mario Kart and Pokemon games, so, people expecting 20M sales are going to be disappointed, in my opinion it will be closer to 15M. But who cares, a mega impressive result for the franchise and Nintendo.