I doubt that will ever happen. I'd love it if they would just do that for some post-purchase fee. I love my AWD, but knowing what I know now, I'd totally upgrade to the P if Tesla offered it for some buy-up fee (similar to what they do for AP and FSD). Lots of folks will have $7,500 - $10,000 (+) cash in a few months, and surely I can't be the only AWD purchaser that would upgrade without question if given the opportunity.
I know all that stuff about binning the motors (and possibly the inverters) but from what I've read the variances would be so small as to not be worth the effort. It seems more likely to me that Tesla is just software limiting the AWD models to keep production simple. Why spend more resources sorting through parts when Tesla's biggest focus is on production throughput. I think if they can get 11-15k more profit per unit by flipping one bit, they would just to that (and I think they are). So why not offer to flip that bit after purchase too?