The Vinesauce playthrough is complete, and one thing that it's definitely shown is that the script still needs some editing. Just looking at the final encounter with Kefka raises some questions:
Why did you have his intro line say "Welcome, fools!" like the Sky Render translation, rather than either the Woolsey/GBA one?
"I knew you'd make it here, so I've prepared some suitable entertainment for you!" is unchanged from SNES and incorrect - I'd recommend "some suitable remarks" or similar.
"I will exterminate everyone, and everything!" and the whole back-and-forth about the temporary nature of life isn't changed from SNES. "And you've found your "joy" in this world that is so close to death?" is a rewrite of the Sky Render translation.
"Now for my next trick, I will make you all...disappear! Say goodbye to your sick little reasons for living!" doesn't quite convey the intended message, since he doesn't attack the party. I'd go with something like "Your sick little reasons for living--for my next trick, I will make them all disappear!"
"I command the greatest power in the universe! You are all helpless before me!" is unchanged from the SNES. I'd go with the GBA line, or change the second line to something like "YOU are HELPLESS and HOPELESS!
Those are my thoughts for now. I hope you take them as intended - to improve the work. If you want more suggestions, I could look at the script, if you wish.