For the Vita and Wii U, Epic used Epic Citadel as their test project IIRC.
Using Unreal Tournament as a test project makes a lot of sense, as it's small enough to port more easily, and is also a fairly demanding game, so they should run into most of the development hurdles you would with a real project.
I have no idea if Epic will support the Switch with games or not, but if they did, I would probably expect Fortnite, SpyJinx, or even Paragon well before Unreal Tournament, given that's such a barebones shell of a game.
Unreal Engine 2.5 was an Epic creation. It was what they named the engine for Unreal Championship 2 on the original Xbox.
Wait, when did they use the Epic Citadel on Wii U? I distinctly remember the Epic Citadel demo live on stage back at the PlayStation Meeting of 2011, but nothing of sorts for Wii U.