From Serai developer:
Grin would require interactivity to receive coins and would be incredibly problematic for that reason alone
To my understanding, there aren’t slatepacks allowing a recipient to receive GRIN without participating in the recipience. Please, feel free to prove me wrong.
As for why it’d be so problematic, it’d force a threshold signing protocol onto all received coins. That’s just computationally expensive and quite annoying to flow. Not necessarily prohibitively expensive though.