I haven't actually seen a full fledged Final Fantasy 6 hack.  I think it'd be interesting to see if people could hack it into another character's "point of view" in the story.  Or even add new characters (though it is probably hard).

I was thinking about this, how about a FF1 hack with a Kingdom Hearts twist? I'd be pretty cool to see the KH characters on the NES, and controlling Sora, Donald, Goofy & Mickey (or Riku) from the start. I know it'll be big job to pull it off, but damn a hack like that woulda got so much attention... ^_^

Hey Goonie, that's a good idea. And actually, it wouldn't be that hard. With FFHackster, you could do almost all everything required. Only a very small ammount of ASM hacking would be needed.

However, I'm not sure that Final Fantasy would be the best engine for such a project. The thing is, Kingdom Hearts is an action RPG and Final Fantasy is a Turn Based RPG, so while you could make it look like KH, it wouldn't feel like KH. I'm not sure what to recommend instead, but perhaps the Mana Series would be a better fit. (Of course, if you're dead set on NES, I have no idea what to suggest.)

That said, if you don't mind the change of genera, you could proably do it yourself using FF. As I said, FFHackster does practically everything you need and I'd be willing to help out anywhere it was insufficent. I don't think it'd actually be that hard. For sure, it'd be a lot of work, but I don't think it'd be that difficult.

I played this translation the last year a bit.
I is OK for hacking(I may be wrong)but 2 chars share a sprite animation.
This is a bigger game,but there are more big NES games which are
not much documented like FF3,DW IV, Doraemon 2,and a few more.

This might be a bit outta hand, but how about a hack GFX of City Connection? Goofing on GTA: SA, Carl needs to put green paint all over the world while avoiding the cops and Officer Frank Tenpenny (The Cat) Carl would be riding in a green Grove Street lowrider LOL!

Karatorian: oh okay, yeah I was thinking about that. There is a FF hack I've been wanting to work on in a long time, the thing is I never really got around into changing anything but just a few words. I'll see if I can get to change a few places this weekend.

I've had lots of ideas for a while about moving characters into different games.  If I had the necessary skills, I would do it.  Some ideas I've had:

Mario in Castlevania:  I was able to get Mario's graphics into Castlevania, but making him behave like Mario would be a different story.  For bosses, he would have to kill them with fireballs.  Mario would also need either a new graphic or Simon's legs to walk up stairs, and collision detection, running speed, the whip, and all kinds of physics would have to be changed altogether.  I've been told that it would be easier to just hack the Castlevania graphics back into Mario.  However it would have to be done, I think this would be really cool.

Mario in Sonic the Hedgehog 2:  I know similar things have been done; I know that Mario has been in Sonic 1, but I think it would be really cool for Mario, with all of his movements and actions kept the same, to be in Sonic 2.

Sonic in Super Mario Bros.:  The only way that you could do this and make Sonic look and act like he should would be to hack SMB's graphics and put them into Sonic 2.  Is this even possible?

I've often thought about a hack of Chrono Trigger in which you battle all the same major boss enemies, except they are heroes from their time lines. Their purpose... to undo what Chrono and his friends have done in an effort to stop their home worlds from collapse do to the paradox. Crazy, I know, but I think it wouldn't be too bad.  This hack would be between Chrono Trigger and Chrono Cross.

Here is a hack I would enjoy very much -
Final Fantasy Legend II:  Remove/stop the continuous screen-shaking effect that occurs after you beat Apollo. 
Reason:  There is more gameplay after him and it is very nerve-wrecking watching the screen shake as you continue to play and train your chars - especially if you like to backtrack to other areas, as the screen shakes persist no matter where you go.  It would be awesome if someone with the knowledge could remove this effect.