Is this confirmed working?
I have a modded and unmodded switch, but don't really fancy this in one player mode...
Can a modded switch link & play with a modded one?...
I have no idea about can modded switches play each other, but for the official game there is this. I don't see why it would matter that the two switches are modded since it's offline but I could be wrong.
Does Mario Kart Live: Home Circuit have multiplayer?
Yes, Mario Kart Live: Home Circuit does have multiplayer. But it isn’t exactly the kind of multiplayer you might expect from a Mario Kart game. Since the game does revolve heavily around the physical toys, everyone is going to need both a Nintendo Switch and an actual kart. There’s also no online that we know of, which means everything is going to be done locally.
So you would need to buy two or more karts but that's if they sell them separate from the game or how much they cost. I assume they do or else this modded release is completely useless. The game doesn't play without them.
From the modding community about the release I only get more questions and no answers yet. You can buy a kit but I think they are mostly sold out everywhere unless you want to pay $200 on from a seller on Ebay or Amazon. I know I'm not buying one period thus I'm just completely passing on this game.