Particle Argon is the first board I’ve seen with the single core version of ESP32. It also happens to support Bluetooth 5 via a Nordic chip.
It’s only using the ESP32 for wifi comms. There’s no way (officially) to re-program the on-board ESP. Which was kind of disappointing. But I suppose it makes sense in the context of their Mesh family of devices (Argon, Boron, Xenon) all standardizing on the NRF52840. I’m guessing they got a good price on the single-core ESP32s, and figured it was worth it for the faster speed and hardware crypto acceleration for TLS?
if by “officially” you mean within confines of particle ecosystem , then correct. however adafruit has a bootloader for experimenting.
AFAIK, they’ve now switched to the dual core version of ESP32.