The ESP32-S31 is the first Espressif chip with an MMU, and Espressif just shipped an official Linux BSP for it built on Buildroot. That pairing (RISC-V, MMU, 16MB PSRAM, $3 ballpark price) collapses a boundary that has separated MCUs from MPUs for thirty years. The boundary was not about clock speed or flash size. It was about whether the chip could run an OS that provides POSIX, shared libraries, and a standard package manager. The ESP32-S31 can.
Firmware teams maintaining custom FreeRTOS or ESP-IDF applications can now target a standard Linux BSP. That means CI pipelines built on Docker images instead of proprietary toolchain installers, and standard debugging tools (gdb, strace, perf) instead of Xtensa-era workarounds. The build target changes from a vendor-blessed SDK on a proprietary RTOS to a Linux kernel plus rootfs built from source, which is a maintenance footprint reduction for any team running more than a handful of device variants.
The loser is the low-end application processor market. NXP i.MX 6ULL, ST MP1 series, and similar parts exist specifically to offer Linux capability at prices that commanded a premium over MCU-class silicon. That premium disappears when a dual-core RISC-V MCU with an MMU costs the same as a mid-range STM32. The BSP is a developer preview, but Espressif has a history of shipping developer previews that reach production stability within two product cycles. Budget 12-18 months.