Just in time for it to be murdered by Mario Kart? =)
Nah. MK Wii is big, yes, but not as big as Brawl. Brawl has been running on a hype machine for nearly 2 years. MK Wii, on the other hand, was barely announced at last year's E3 and save for all the info coming out of GDC Nintendo has been quiet about it.
The game will still be a hit, yes, but its hype is small when compared to Brawl's.
Plus, I still don't see the game being released in April, no matter what the rumors may say.