Nobody seems to have filed a formal issue with platform-espressif32 to have this implemented, all talk is in the forum where the devs overlook it. I’ve opened one at Add LittleFS and FFat filesystem support · Issue #570 · platformio/platform-espressif32 · GitHub now.
Further, since nooone seems to have done this yet for PlatformIO, I implemented FatFs for Arduino-ESP32 and PlatformIO in a modified example repo, using mkfatfs (same as the Arudino IDE plugin uses) and a bit of scripting. See working example repo at GitHub - maxgerhardt/pio-esp32-fatfs-example: Example for how to use a FatFS filesystem with PlatformIO and an ESP32..