Nintendo's strategy (should be);
Cultivate young or undeveloped IPs with better marketing
Revive old IPs that have potential
Create new IPs that create even more variety
Bring in 3rd and 2nd party exclusives to supplement (new IP and old IP)
Market everything.
They are already doing most of this. The last one is what they failed at (really hard) in 2012 and 2013 and January-March of this year.
If I had to pick just one at this very moment, I would say old IP. Nintendo is already absurdly diverse, they just need to show it more through marketing. Heck, even some of their "major" IP have been hamstringed by horrid marketing (Metroid)







