I've been playing around with the emulators for the Genesis Flashback 2018, and I was able to unlock the extensions on the SD Card and give an alternative for Genesis Plus GX (Picodrive).
Genesis Plus GX still the most complete emulator, and it will run Genesis (.bin/.md), Master System (.sms), Game Gear (.gg) and Sega CD games (.bin/.cue or .chd). For Sega CD support, copy the BIOS files (BIOS_CD_U.bin, BIOS_CD_J.bin and BIOS_CD_E.bin) to the same folder as the games.
Picodrive is faster than Genesis Plus GX, and it will run Genesis, Master System and 32x games. I couldn't make it run Sega CD games, and you will lose Game Gear support. Picodrive also apparently fixes the issues with PAL games (at least Master System games run at the correct speed). To make Picodrive work with a 6-button controller, you will need to copy both .ini file to the root of you SD Card.
Please don't expect Sega CD and 32x games running at full speed. While they work fine, you may have some sound issues when the framerate drops.
If you don't like Picodrive, you can revert to the original emulator installing the Sega CD update.
Thanks
@dcuk7 for sharing a dump from the EU/UK version.
P.S.: (1): While I did some limited test and we are not messing with the 'vital' OS parts, I can't guarantee the updates are 100% safe.