It looks like to make it work with the file provider API in the upcoming Kodi we can't use extras. There is an example of ppsspp working without it
xbmc/xbmc#24075 (comment)
Not sure if other emulators can be called the same way.
Retroarch needs at least two Params I think but only one needs to use the file provider API.
Emulators that work with dataURI (require IAGL launch command change)
Emulators that don't accept dataURI (would need workaround or PR on emulator)
Emulators that can't accept a content: url at all