I think that the RAM in the ESP8266 will be enough to handle up to 16KW devices, for bigger devices I might have to upgrade to the ESP32.... Or maybe I can upload the hex directly to a file onto the SPIFFS file system. Then I can handle hex files bigger than what the largest PIC requires.

But for the time being I'm happy with just hardcoded support for the 8Kword 16F1705 device.

I have hooked up the ESP and the PIC with a LED on a solderless breadboard. Time to start coding - this shouldn't be too hard. The Microchip LVP protocol is rather simple and have decent docs.