It runs fine on Xbox One, which doesn't have the frame-pacing issues of the PS4 version.
People thinking UE4 is going to magically make the game run better than the current version on Luminous, let alone run the game better on Switch... UE4 has its own performance problems on Xbox/PS4.
A UE4 open world game (ARK) with similarly dynamic lighting and weather on PS4 runs at
640p on base mode,
max res of 720p on detailed mode, constant tearing, fps dips to 20s, noticeable object pop-in. The normal mode on PS4Pro even runs at a locked
720p.
http://www.eurogamer.net/articles/digitalfoundry-2017-ark-survival-evolved-performance-analysis
This just seems like Tabata throwing out a bunch of various options that they have. Would be interesting to see them downscale the game on UE4 for switch but considering their focus is soon to be on the next-gen console cycle, I expect this to go the same route as Tabata's talk about XV using Just Cause streaming tech.