Why I'm wondering is that:
1: I'm just interested. I don't have one.

2: If there is a way to replace the BIOS via that expansion port, could someone come up with a card that only replaces the BIOS (not necessarily any other added features) with a BIOS that allows homebrews?
I've seen people talk about burning a chip with 2 bytes changed and replacing your BIOS with it (lots of unsoldering and soldering), which is an issue for most, but I'd consider paying for a cart I can slap on my FZ1 to allow homebrews. I have a Cuttle Cart II for my 7800 and a MultiCart for my Vectrex, so the concept isn't foreign to me.

I'm just thinking out loud here...
desiv