I'm kind of interested in this too. The Plaid uses permanent magnet DC motors, but the pre-refresh S uses AC induction, right? Heck don't all previous Teslas use AC induction? Notwithstanding the missing third motor in the back, it seems like it would be a significant jump in complexity from a development (and production) standpoint if the LR used AC induction and the Plaid doesn't.
I feel like, as others in this thread have pointed out, the only major mechanical difference between the LR and the Plaid is the third motor and they try to make that fact less obvious by just not saying much about the LR (and also not delivering any, awwww).