GenGAME is spreading a rumor that Retro Studios, the Nintendo-exclusive developer best known for the Metroid Prime trilogy, is, at the behest of Nintendo, "creating game engines for Wii U and helping other developers implement them. " According to the rumor, Retro convinced Epic Games to reconsider bringing Unreal Engine 4 to the Wii U. Epic has previously said that while an Unreal Engine 4 game could most likely be ported to the Wii U, they felt Unreal Engine 3 would be a better fit.
More sophisticated game engines available to developers result in slicker, better-looking games. If true, this rumor would indicate that Nintendo is very serious about winning over third party publishers, as Nintendo's own games, which have always emphasized gameplay experience over slick effects, rarely push technological boundaries.
The downside of this rumor is, if Retro is spending all their time on game engines, they may not be working on a Wii U game right now.