Personally I'm really stoked about the Uno finally getting a 32 bit ARM core. And an M4 at that! I would've thought maybe a M0+ (like the RP Pico) on the Uno and perhaps an M4 on a hypothetical future Mega update.

Good stuff from Arduino. The AVR on the previous Uno revs was getting quite outdated. Simple to use yes, but the Arduino environment mostly abstracts over that and only "power users" ever need to dive into peripheral registers and whatnot (eg to use interrupts).