Yep, I want Eyefinity too
I'm still waiting for it to unlock but afaik:
1) Eyefinity/surround resolutions do work, i.e. you can run the game etc
2) There's already a version of dead island helper for riptide that you can fix the fov for a better widescreen experience :
http://steamcommunity.com/app/216250/discussions/0/828937261940292800/3) The thing that seems to be broken is the HUD. As there are new elements in the HUD I don't think that the old set of fixed HUD files will work, however as the engine is the same, one might use the same technique on the new HUD files. I don't know if that is correct so don't take me at my word.
I'm going to have a go (if I can figure out how the original fix was done).
4) The best way to get this done faster is to moan on the steam forums in:
a- The official issue thread (watched by deep silver people) :
http://steamcommunity.com/app/216250/discussions/0/828936719123525994/b - Create a new threads and complain
I really, really want an eyefinity fix for this game
EDIT:
The folder structure is different in riptide. There is no menu folder in
C:\Users\your_user_name\Documents\DeadIsland\out\Data
I can't immediately see how to apply the old fix