Why should this be included in the repository?: Mednafen is a very popular command-line (yet very easy to use) multi-system emulator. Supported systems are NES, SNES, PS1, several SEGA systems and others. Works much better and has better compatibility with PS1 games than for example "pcsxr" provided already in repositories.
Is it Open Source: Yes - GNU GPLv2
How many users do you anticipate will use this software? Dunno... A lot of?
Link to source tarball/zip file: https://mednafen.github.io/releases/files/mednafen-0.9.44.1.tar.xz