If Nintendo can have a successful console that has no restrictive barriers that prevent third parties from making the games they want, then it will be very hard for Nintendo to **** up third party support. The N64 and Wii had too many hardware restrictions to allow third parties to make the games they wanted to make. The Gamecube just didn't sell well enough.
It isn't really that Nintendo had to go to the trouble to seek out UE4, they just needed to have hardware that could do that stuff Epic wanted to do. Epic is a business. If the Wii U hardware will let them do what they want to do and they think they can make a buck doing it, they'll do it. Nintendo wouldn't even need to seek them out, they would just come. Third parties didn't shun the Wii because they hate Nintendo or anything like that. They wanted to support the Wii because it sold so well but they could not include it in multiplatform development so they had to make a unique Wii product and they only have so much staff so the b-team got it and the resulting game wasn't much of anything and it didn't sell so they gave up. To make money on the Wii they needed a seperate team just for Wii games and that team had to make product with comparable quality to their other games, which they already had their best guys and the bulk of their budget going towards. It just didn't seem worth it to them. Nintendo was essentially asking everyone to make every game twice or make twice the games they wanted to make.