WRT to Perth rectangular stadium, hopefully the heritage status of the western stand will be waived.
It can only exist due to WAFL heritage, and they make look to have heritage status maintained to obstruct RL, ala AFL with Stadium Australia..
But if they're serious about a rectangular stadium, it can't stay.
I suspect any new (western) stadium will be stand-alone with the possibility to curve into the south stand at a later date. The corner into the north stand cant fit and will likely remain a gap for the big screen.
They will likely cannibalize the western car park too.
I also suspect it will likely be design like the western stand at Parramatta, i.e. wall-to-wall corporate facilities