I would stay true to the original game to make it as similar as possible to the arcade. I don't see the point in adding fictional characters. Better use that time to improve other things.
I thought all characters were fictional. 
The point is to have fun of course, you may not see the fun of it, but maybe the developer sees it (or not). The developer is the only one who can say if it will be fun for him to do it.
I don't see the point of making a game as similar as possible to the arcade today. It was something really good in the 80's to have games as close as the arcade as possible, because we didn't have emulators to play the arcade version at home. I already have the arcade version here, running in a emulator, and the same game running on SNES / PSX / Mega Drive and others. They all try to be as close as possible to the arcade. So I don't see a point of having another copy of the arcade.
To me it would be really amazing to have something new that the arcade does not have.
Pointless Fighter, together with SMW are the best games for MSX, through all generations.
PF is the best SF2 port for an 8-bit machine, better than Master System version, IMHO.
Any improvement/addition to the game would be greatly receiveid by the community. Do whatever you want to have fun. It's up to you. 
GhostwriterP wrote a super cool tool and a piece of asm code
Yeah, those were the days 
Still think a beat'em up would be more fun than street fighter... we can have our own Paprium
Was there a thread on msx.org about it or something? If so, got a link?
I worked several months on it, and got to this point:
Downloadable Rom:
https://www.dropbox.com/s/1mzs4ia5itikril/streetfighter.rom?dl=0
I've tried the rom with MFRSCC+ RomType AUTO (SCC type).
Is it normal that the opponent is always "garbage"?
AH, I've also tried the game with MIDI-PAC V2. WOW!!!!!
