Sudden death is good for takedown and TDM, but takes all the objective play away from the rest of the modes. So I have a few ideas for the final rounds.

For Splitball: 3 balls spawn all at once, but only 3.

For fire c******: Arm, Defuse, countdown, and the round timer are all cut in half.

For Domination: score limit in half, capture time doubled.

For Hot zone: only one capture point, and the capture time is doubled.

For KotH: score limit in half and increasing spawn timers like takedown.

That's all the modes I can remember. Hope this inspires something.