With Sing On Tour in Osaka, they explicitedly use songs directly used in the original film. If they'd make a Sing show, I'd assume they'd mix songs featured in Sing 1 and Sing 2 for the sake of it.
To bring up on the subject of Grinch, it still is Dr. Seuss. It's shocking that a larger presence of the IP hasn't been at USH on a permament basis (and not a seasonal one). Interestingly enough, I wonder if a Grinch attraction...doesn't, have to rely on being in Christmas. Controversial words, yes, but hear me out.
It isn't the first time that the subject would be of intrigue, as Grinch has occasionally popped in other forms outside of Christmas. Most famously, Grinch Night as the odd man out. Perhaps Universal Creative Hollywood had a Grinch concept that could work, with no use of the holidays as a full on element?