Probably the PS3/360 version with a bit more polish.

Probably it's own "special" version.....can't be the SE because I doubt the Switch can handle mods

Well, the footage comparisons showed the Switch version being very close to the SE version of Skyrim.

PC Special Edition Top - Switch Version Middle - PC Original Version Bottom

http://gearnuke.com/elder-scrolls-v-skyrim-nintendo-switch-vs-pc-comparison-confirms-improved-visuals/

Based on the footage, it's the special edition.

knowing Bethesda, it's probably PC footage

if you're talking about specs, a pc with less specs than the switch can handle mods.

Maybe it's a Skyrim Switch edition, which is better than the standard version but not as demanding as the PC/PS4/XBOne Special Edition to keep perfomance in check?

Mods can run on PCs with lesser specs than the Switch.

it has been confirmed by comparing screenshots that the Switch version shown in demos so far has been much closer to the remastered "Skyrim" than the older version. Enhanced detail and light effects compared to the original game.

Obviously we won't know exactly how similar until we see the final version when the game is released though