I actually had this same thought a few weeks ago (along with the lack of auto reply module now that SBW doesn't support BNet whispers) and began to make my own. It's stand alone at the moment (uses LDB to display the data) and because of that is taking a little longer than I thought to get it right (after writing the combat detection for this mod, I have so much respect for the creators of BW and DBM. I really wish Blizzard would pick a method and stick to it. Garalon is 'boss5' Blizzard really?).
Anyway, I'd be more than happy to share it with you guys when I've ironed out the bugs and such, although I can't guarantee it'll function perfectly as it's not attached to BigWigs. It does however add a bar into BW to display the time remaining to your record kill. Here's a picture of how it looks if you're interested.