Yesterday it occurred to me that Final Fight for SNES may have some secrets, such as two player support, I decided to investigate and the results speak for them self:

After some reverse engineering of the code and a few minor hacks I was able to enable two player support.
For those that are interested here is the code, works with CRC32(0x4CAB21DB) Final Fight USA and xkas06. I dumped my own cart, not sure how common this version of the game is, sorry.
lorom
org $01a643 ; (original code - ldx #$0d00, jsr $a542, phx, pld)
JML hijack_player_init
org $01a57b
RTL
org $01a651
RTL
org $01a5f2
NOP
NOP
org $00ca67
ldy #$0112
org $00c9ea
JML hijack_player_sim
player_sim_hook:
jsr $cc45
jsr $cfd3
RTL
org $208000
hijack_player_sim:
rep #$20
lda #$0d00
tcd
sep #$20
JSL player_sim_hook
rep #$20
lda #$0d80
tcd
sep #$20
JSL player_sim_hook
JML $00c9f8
hijack_player_init:
LDX #$0d00
JSL $01a542
PHX
pld
JSL $01a64b
ldx #$0000
phx
pld
LDX #$0d80
JSL $01a542
PHX
pld
JSL $01a64b
ldx #$0000
phx
pld
JML $01a656
And here is a link to a very quick disassembly with minimum comments:
https://pastebin.com/PNiGy6aQPlayer two can walk around, but he shares vram space with player 1 currently so moving either character corrupts the other. There is no hit detection for player two yet, nor can player two advance the stage. However I believe both of these issues are resolvable with a few more minor hacks.
I would like to propose a restoration project for Final Fight SNES. Add full two player support, fix industrial area, add guy to the roster, and remove slowdown.
As the game already has the tile data for industrial area we just need to demake the area's arcade graphics. Guy support is partially built into the game already, porting him over from Final Fight guy shouldn't be too hard. Slowdown may be solvable by switching to fast rom, it may need additional work optimizing code, not sure yet.
Just wanted to get this out there, if anyone would like to help with the project with either graphics or code please let me know.
-Grego
Edits: Added disassembly pastebin and CRC32, removed palette test code