Final Fantasy VI has actually seen several ports, rereleases, graphic updates, and fraudulant sequels. I can give you some information on some of the lesser-known ones. As Final Fantasy VI Advance seems to come up in every other paragraph, I'll assume you've got that for now.
FFVI-2: The Shadow of Light: A few years ago, FFonline posted a story about a Shadow-themed sequel to Final Fantasy VI. It was an April Fool's joke, sure, but hey, I would've bought it. (Although, let's admit, when it comes to FFVI, I am Square-Enix's slave.) The story followed Shadow, which is probably the best choice they could make- except that there's a place in the game where he can die permanently, and his ending in FFVI is unclear, to say the least. Anyway, in the course of the game, Celes and Locke had gotten married, and Sabin was left in charge of Figaro. Shadow was admitted to be Relm's father, and he plays through the game unmasked. If you want more information and pictures, there's a site here. But be aware, I'm pretty sure that Square had nothing to do with this "Sequel" and that it was all a hoax of FFonline. The images just don't look right to me.
FFVI SGI demo: You may have also seen a few pictures of the Final Fantasy VI cast rendered to about Final Fantasy VII quality and wondered where they came from. Was that a sequel as well? Was it a remake for the Playstation? After Final Fantasy VI was released, the Square team had their artists show off their rendering prowess with this demo. It could only work on Silicon Graphics systems and it was assumed that this was what the next Final Fantasy for N64 would look like. Later on Square decided that the N64 couldn't handle what it wanted to do- perhaps because of this demo. Final Fantasy VII was launched on the Playstation, and that game made it the system for RPGs. The SGI demo featured Locke, Shadow, and a bikinified Terra fighting a rock monster. You can see it in action here.
Now, you may have noticed, but Final Fantasy VII is no longer a game but a franchise in its own right. There's a pan-Final Fantasy action platformer thing on the horizon, Kingdom Hearts will be getting its sequel, and Final Fantasy VI has only recently been ported to the Game Boy Advance. With a Final Fantasy IV DS port on the way and titles like Final Fantasy Tactics: The Lion War just recently released, it seems more likely than ever that we'll see Final Fantasy VI reincarnated in the third dimension. Heck, Setzer's already shown up in Kingdom Hearts II.
My feelings about this are mixed. On the one hand, I strongly feel that Final Fantasy VI is pretty damn good as is. The sprite graphics, while they are sprite graphics, are very well designed and are used both in and out of battle for flexible storytelling. (I much prefer them over Final Fantasy VII's.) But of course, graphics are the least of an RPG. And that's really the point: the story and gameplay of Final Fantasy VI are fine as it is. It's got a beginning, middle, and a satisfying conclusion. Nothing really needs to be added; it is what it was designed to be.
I've included an approximation of what Locke would look like in 3d, kindly provided by Stacey Anne, who is good at these things. Note the bandana.
Stronger still is the possibility of Final Fantasy VI characters in Kingdom Hearts or Final Fantasy Dissidia. I'm still not sure what either of these things are, really, but Dissidia looks like it's some kind of Super Smash Bros clone? In any case, it so far features Nomura redesigns of characters from the original Final Fantasy and the ninth installment. It seems pretty likely that some character from Final Fantasy VI will show up, and Locke's both popular and one of the story's most important characters. And I wouldn't be surprised if the Kingdom Hearts franchise continued until every single Final Fantasy character possible turned out somewhere. I have a pretty good idea of what Locke would look like if he turned up all Nomurified, and needless to say the result isn't pretty.
What are you saying? "That's a poorly photoshopped picture of Squall, not Locke." To which I reply, "Oh, snap." Really though, think about it. Squall and Locke have the same color hair, at least some of the time, and Squall's Kingdom Hearts outfit is basically the same as Locke's, but with all the unneccessary belts and zippers a Nomura character design requires. I'm sure Locke would come with a trademark annoying symbolic medallion, which the crazed fan can purchase fro Square Enix, Inc. for only 2,000 Yen or so. It...well, it probably wouldn't be Griever, but we can ignore that for now. Furthermore, both are 25, strangely up beat despite seriously angsty pasts (seriously, what's up with that, Leon?) and I'm sure Locke could go by Cole or some such nonsense. And hey, they also both look a lot like Gackt in FMV closeups!
Okay, I think I need a break now...