A few notes on the switch from RP2350B to STM32H563:

v1 of the board had the RP2350B, which had dual-core, 2x SPI, 2x UART, 2x I2C, and PIO support, which was genuinely useful for the deterministic timings we needed. The issues we hit, though:

• No Ethernet support, which would mean an external PHY/MAC chip like the W5500. That'd work, but you'd also need an extra SPI bus for that
• That brings us to the lack of peripherals in RP2350B. You can use PIO, but PIO state machines are also not unlimited, and if you have to use it for SPI/I2C/UART, you can't use it for something else anymore
• The RP2350B has no internal flash, so you need an external flash, which adds floorspace on the PCB, an extra BOM item, extra feeder fees on low volume, etc
• The RP2350B doesn't have built-in wireless. If you want to build the pico2 (RP2350B + wireless) architecture yourself, you would need to recertify the Wi-Fi. If you want your MCU on your pcb to be RP2350B, you'd still need an ESP32 or Pico2 module on your PCB separately if you want WiFi without having to recertify the WiFi module

That's why we moved to the STM32H563ZIT6. It's a big step up, but the gap is smaller than it looks once you count the full architecture:

RP2350B + boot flash + inductor is around 3 USD (low volume, during prototyping). You also have to account for extra feeder fees for the components you need, specifically the RP2350B, including resistors for the USB pins that other chips have internally. This disappears, of course, at volume, but a unique part count in a BOM can bump you to higher fabrication tiers.

STM32H563ZIT6 with its internal flash and no external parts: 7.70 USD (prototype quantities) and around 5 USD at volume. That's a big jump, but you get a lot in return for external parts that you don't need. You now have MAC support for Ethernet, and you don't need the W5500 (which is ~2.7 USD at low volume). You have the extra SPIs/I2C/UARTs, but you lose the PIO. 

Conclusion: the RP2350B is great at the low price level, but you might outgrow it quickly if you need Ethernet, more SPIs/UARTs/I2Cs, and the external components make the price difference smaller than you think, especially if you take into account that there are a lot of other MCUs in between the price point of an RP2350B and an STM32H563ZIT6.