I would love to see the next Everdrive for NeoGeo Pocket and, after that, for WonderSwan.
Next, for Atari 2600, Atari Lynx and Atari Jaguar.
After that, maybe some revision for the Turbo Everdrive.
But I would love to see some kind of Everdrive SS (for Sega Saturn), not to load ISOs, but to do some crazy features, like:
1) Have the ROMs of Ultraman and KoF'95 cartridge pre-burned and ready to select;
2) Suport for RAM expansion, with 1MB and 4MB selectable (or disabled);
3) Backup cartridge support (to be used by the compatible games and the Sega Saturn system);
4) Data Bank (for saves) support (separated from the Backup cartridge function);
5) Import/Export saves from the backup / data bank to a conected SD card;
6) Homebrew launcher from a conected SD card;
7) Region lock breaker;

Action Replay codes supported.