I have laid out an IDE interface with an UberGROM powered by an ATTINY84 - that'll give me 8k of GROM on the cart, which is plenty to bootstrap and maybe even run the game.
I'm expecting to need 32k to run, but I guess we'll see.
Anyway, I've still got a long way to go.. hopefully using this will let me work out the kinks and prove the hardware and software both. My first pass, I'm just going to load EasyBug on the GROM so that I can poke at the CF card manually.
I was silly and laid out the PCB before getting the TI cart outline, so I made it way too tall. Still, I think there's a good chance it'll fit. One more night should be enough to get me there... then I can order some and we'll see.