I don't even really know how to respond. A lot of people have been talking about why certain properties would work, (including Roy Conli) saying that the 'themes' match up in KH with a certain property, and it's usually something like FRIENDSHIP or FINDING YOURSELF or BEING KIND AND UNDERSTANDING, when these are themes present in almost all media.
Sofia the First is made exclusively for a very young audience. If you enjoy it, that's fine, but it doesn't synchronize with Kingdom Hearts in any way. Unlike Winnie The Pooh, which is a timeless classic, with tons of effort put into every production, Sofia is a flash in the pan kids show. That said, I'm not huge on Winnie The Pooh either, but I find it enjoyable to watch with my nephews, and the 2011 film is genuinely very funny.
While a good portion of KH players weren't keen on the Pooh world, (which is why it's optional) a better portion were pleased by it's inclusion because it's a multi-generational beloved classic. Children don't typically play KH these days, so your average player is going to wonder what the hell "Sofia The First" is, and promptly avoid that part of the game. I sure as hell would. I thought Atlantica in KH2 was cringy.
So, in short, no, I don't thinkg it would be a GREAT idea for KH3.