Rdna2 did not make it into mcu3 for 3 and Y. That remains to be model S/X exclusive. So the inboard graphics will be from the Ryzen APU which is still 3x faster than atom.I'd expect it'd be the RDNA2 GPU (MCU3 has a discrete Navi23 GPU per Ingineerix) that'd be the bottleneck... same GPU parts that go into making the RX6000 series GPUs, and the SOCs on the PS5 and current Xbox, all of which supply can not keep up with demand on currently.
That said- I expect the catalyst for Tesla getting their ducks in a row for widespread upgrade offerings there would be when (if) they launch the theoretical app store where folks can buy current AAA games and whatnot that'll require the newer MCU.
Speaking of that--- anybody know what the onboard storage is for the MCU3 unit? If they're serious about doing AAA gaming it'd need to be MUCH larger than what MCU2 offers...unless they're planning to do a "bring your own SSD via USBC" thing--- but if they put a legit large storage device on MCU3 it'd be a large clue where they're going with it.