Happy T'Day everyone,
here is something I cooked up with RevEng (bBasic support will come). It's a board that can handle 27C128, 27C256, 27C512, 27C010 and 27C020 EPROM's and it uses a 22V10 PLD to do the bankswitching (sorry, no 20V8 and not backward compatible with any other board). Every single pin on the PLD is used for 256K, so even if you have a suggestion, it's too late. It also supports SARA chips, so in essence, it's a 10 in 1. Two new bankswitching schemes have been designed, RevEng already has a locally hacked copy of Stella (once flushed out, Stephena will likely put it into the official version).
F4, F4SC, F6, F6SC, EF, EFSC, DF, DFSC, BF and BFSC.
DF/DFSC is the new 128K bankswitching scheme, touch $1FC0 to $1FDF to select 32 banks.
BF/BFSC is the new 256K bankswitching scheme, touch $1F80 to $1FBF to select 64 banks.
Here are a couple pics, both of the routed new board and my hacked up SARA board to deal with all the above mentioned methods (currently configured to 256K, no SARA).