This would be valid if you’re asking for CarPlay to take over the entire Tesla screen.
But as you already know, that’s not how a realistic scenario as to how CarPlay would function on a Tesla if it were a feature.
... I'm not sure why you think running in a window rather than full-screen (which again, the Tesla software
already does across multiple apps and Carplay inherently supports doing in interfaces for years now) would be make any difference whatsoever.
Especially since what it'd be running in that window is likely to be
less demanding on the car than some other things it already runs inside windows.
In short, there's absolutely
zero technical reason whatsoever Tesla could not add carplay support to their vehicles.
They have, very clearly and intentionally, (and consistently for years now) made an intentional business decision not to do so.
We can speculate why...
Tesla thinks they can do better with just their own native apps developed in-house (Musk has often made remarks about how much better than anything else their system is gonna be.... but it's WAY the hell behind schedule getting there... they still haven't figured out how to add Waypoints to the nav system- something Garmin figured out 15+ years ago and Tesla has promised is "coming really soon" for years.... ditto reading text messages...)
Or maybe...
Tesla wants to keep their ecosystem entirely walled off because they eventually want to monetize their own app environment (there's been a lot of speculation on this- Musk has commented that it might make sense as the fleet gets bigger....) though here there actually IS a technical obstacle that wouldn't be one for Carplay... the car doesn't have a massive amount of onboard storage. This limitation has already caused an issue- it's why Cuphead only contains the first area on a Tesla instead of the whole game. The USB 2.0 ports in the front aren't nearly fast enough to solve this issue either. Even worse, the storage it does have (32GB of eMMC) is not replaceable with something larger. It's soldered to the board, not socketed.
Which is how we know there's not gonna be a whole lot of HUGE DEMANDING SOFTWARE coming down the pipe- there's no place to store it.
Ironically of course- Carplay and Android Auto can fix all these issues- since both the processing work and the storage for TONS of apps can be offloaded to the phone.
or maybe...
They plan to offer their own "phone mirror" system--- Musk even
said they were....at the start of 2016... then it never came up again. So maybe not. This was after they'd previously said they were gonna release an SDK for developers that also never happened...but now they're maybe talking about it again in relation to the "walled off app environment" notion...but then back to the storage problem....