Perhaps this is a bit odd thought, but I always felt as mobile products go up in size they becomes less usable in the real world.
Examples were the older 17" MBP from years back, the rumor of iPads larger than 12.9", and yes this 15" MBA.
Right now I see the MBA/MBP13 as ideal for being in a airport or coffee shop setting. There was a lot of discussion about the 14" vs 16" MBP and what is easier to work with on travel. The thought of how awkward a 15" iPad Pro would be with two hands also was discussed. So while people that don't want to spend the money on a $1999 MBP fantasize about a 15" MBA, would it really be that great to use given how compact the current model is for carrying around?
If we assume that the 15" has to weigh more for a larger battery to drive a 15" screen, additional weight if it involves a 500 nit display over a 400 nit display. The cost is going to go up and it's going to be getting close to MBP pricing. Given the upselling of the Mac Studio tactics I wonder if even with the demand whether the negatives outright the positives in this rumor?