Something I'd like information on is whether it is possible to upload a SPIFFS filesystem image to the ESP8266. In theory it might work: It can be uploaded over USB, and according to the logs the flash location changes, but that's about it. PlatformIO also seems to offer an Upload SPIFFS option in a platform that's set to an OTA port, but that could just be it not checking the upload type.
So, what I want to know is how I can configure (or otherwise make) a SPIFFS image OTA-uploadable. I have two main OTA methods: Option One is the default Arduino OTA library, and Option Two is a re-skin of the OTA method-whose-name-is-forgettable where I can upload a file on a webpage hosted by the ESP8266 and it will read the file and update its firmware.
I'm assuming that there's a configuration parameter for this somewhere, but I don't know where to start looking, and the documentation on these libraries has a few very basic examples that don't cover complex or advanced use cases.