PITA
Model 3 Performance
Would be ideal for end user - yes.
but would it be for Tesla which has very specific product - PW which they sell for profit. becaue people would use it as large battery anyway, not for the trickle feed to PW alone.
this would definitely canibalize PW sales. so why would tesla enable feature which in the end would mean less sales for them?
Because if they don't, somebody else will... and they'll lose brand loyalty.
Better to keep people happy within the eco system, by offering scaleability and flexibility.
Not everybody has space or security for a Powerwall