Oh the indecision of it all! No matter how hard I've tried, I simply can't get it down to "only one cartridge". Two is pretty good though, one for 'mostly games' and one, one for everything else...
Your auto-booting 4A DOS made to work from the FinalGROM99 Cartridge.
Note: This won't work on UberGrom...
I zero'ed the PROGRAM list entry in the 4ADOSC.BIN, made a note of the address it normally launches.
Then added a "4A DOS" PROGRAM entry to the 4ADOSG.BIN, this runs a single byte GPL routine 'EXIT' which takes us back to the boot process, and the powerup routine Tursi wrote...
(adding a program entry to the GROM was necessary to get the FG99 to load it)
Then, I since I zeroed out the entry list in the ROM, I changed Tursi's code that searches for the entry point, to just load the known value for 4A DOS, and proceed to his 'LAUNCH' routine.