I'd say Kredits are a must for a Final Smash. Though, I thought it'd be clever to make it appear that the Vs. Match ended ("GAME!") and went straight to the "The winner is..." screen (so, a cinematic FS, maybe even with Kremlings cheering for K. Rool in place of the other fighters during "The winner is..."). And then it could cut back to the fight and cannonballs could start dropping. Or, there could just be fake credits that lift players off the stage. Either one could work.
One thing I noticed a few days ago while playing through Brawl was just how much of an impact K. Rool made, especially in SSE. Not only was he a trophy (like in Melee), a sticker or two, and an optional Stage Builder name, but a lot of Bowser's character toward the beginning of SSE was an obvious homage to K. Rool (stealing the Banana Horde, trying to get rid of the Kongs, all that good stuff). The music that plays before you fight Shadow Bowser is even K. Rool's theme. That's just something interesting I thought I'd bring up.
You can count me as a supporter, by the way.