Azelover hit the nail on the head with his second sentence.
Every company has to look at their resources and optimise their output in a way that will get them the best results. If they add say online to NSMBWii or add a few more characters to Punch-Out!! they'd begin to see diminishing returns on their investments and it wouldn't be worth it.
Sure Nintendo could outsource more in the future however it's not getting them anywhere right now, especially in Japan where their biggest out sourced games include Sin and Punishment 2 and things like Captain Rainbow, both which are examples of games that sold or will will sell poorly in that market.
I think Nintendo need to make smart partnerships like they're doing with Team Ninja for their out sourcing efforts to work effectively but I'd much rather see more internal teams developed in the next 5 years. We've seen second parties already this generation on Project Sora and Monolith Soft (neither releasing anything/anything notable thus far) but I think Nintendo should push towards more EAD groups.
If Nintendo could create an EAD group in the GameCube days (EAD Tokyo, which incidentally has become perhaps their finest group) then I'm sure they have the resources now to expand their development might further.
