To be honest Splatoon has a lot op potential, but a game like this would a need a strong online community to really become succesfull. And i don't see that happenning on Wii-U.

no.

Honestly I'm not sure if it will even see a sequel. Maybe in ~10 years like Star Fox and Pikmin.

I see excactly that happening already. There are too many people more than hyped about this game. And Nintendo does its best to cater us by giving out a constant stream of informations. 

Expect Nintendo to excel when the game gets released...

Would not surprise me. Imo, Zelda is underated in terms of sales.

When you look at Uncharted or Halo they are always close to 10m or above......

The real question is whether Disaster: Day of Crisis will be bigger than Metroid?

Lol, no.

they just announced there wont be voice chat in splatoon. so any core gamers interested wont even look at it.

"Core" gamers have used Skype, Teamspeak and similar stuff for communication in previous Nintendo online games so why should they ignore Splatoon because of missing voice chat?
In most games it's about team tactics anyways and, tbh, Nintendo would just put everyone in the same chat and destroy tactical communication. It might be cool to come up with secret phrases so only your team understands your comments but that'd be something for a fun match but nothing serious "core" gamers want to do.