Apologies for digging up an old post,  I've been working on a new startup.gb for zeigler type carts (am29f040/am29f016 on mbc1 donor with mbc1 ea00 & ea01 on high address lines of flash chip).   
I am trying to get the cart to do a partial erase and rewrite new banks/roms so that it isn't limited to just three different roms controlled by the ea00/01 lines (the mbc1 2mbit rom/32kbyte mode). 
According to the specs: Minimum 100,000 write/erase cycles guaranteed, the flash wear shouldn't be too much of a problem?  If everything works according to plan, i can add some kind of wear levelling so that the sector rewrites get distributed a bit more evenly.
Also, as the initial menu program won't get touched, the risk of bricking is minimised.
I was wandering if anyone else has tried?