Hopefully, we will have a positive answer...
Having a free GNU toolchain for the ESP8266 would be great, of course.
But it is really difficult to get public information regarding the XTensa CPU range, ISA, and even harder to know what is inside the ESP8266 SoC besides the block diagram in the datasheet, which is not detailed enough to be useful. Maybe Espressif could provide a more detailed diagram and a memory map?