I’d love to see a sub-1 GHz member in the Xiao family. I have been told the Wio-E5 is too large to fit on a Xiao board.
I have been playing with the very nice CC1310/CC1350 (first generation) and CC1312/CC1352 (second generation) MCUs from Texas Instruments. The CC1310 and CC1312 include a sub-1 GHz radio. The CC1350 and CC1352 feature two radios: 2.4 GHz for BLE and sub-1 GHz.
The CC1352P comes as a 7x7mm MCU with 28 GPIO, 80 KB RAM and 352 KB Flash.
Resources include Arduino-compatible cores:
and a fork of the Arduino IDE called Energia IDE.