The following info comes from Ubisoft's Davide Soliani...
The framerates seem to be the same for both modes so that's all that matters to me! Should run good enough to work well
You won't even note the difference unless you play in front of your TV. I had expectations of noting the difference (have a 720 old Plasma TV on my living room) while playing Mario Kart and Splatoon on a 1080p TV on my bedroom, and guess what, no difference to be noted while playing. No difference at all with breath of the wild (which runs at a similar resolution). So expect no seriously noticeable difference.
I guess you'll notice it only if your TV is huge or you sit like seriously close to your TV. And I mean noticing it by switching resolutions on your console, not by just playing the game
Yeah: higher resolutions are technically always better, but with these consoles it's always a tradeoff with other considerations (like framerate and post- processing) and clearly the game is gorgeous. I'm happy with it. This is one of the best looking games on a Nintendo system ever: less than half a year into a new console's lifespan. I think the Switch is just the coolest!