Conquest renegade mode?
Basically.. remove the harvester or make it collect less, put capture points like tiberium spikes in the field. Would make for some interesting gameplay as you'd also have to worry more about your income than in the original renegade
A mode I've always wanted and would fit with C&C style
Base building mode, you start with a barracks and a refinery... the base building parts are placed around the middle of the map (of course the enemy team will also be fighting for these). After bring them back to a point in your base.. (say a construction yard) a part of the base will be built giving you access to tanks or base defences.. walls.. etc . If both teams bases have been fully built it goes back to normal mode.. but that's if nobodies lost by then.
You could even make it interesting, if a team has fully built there base, place a timer for a nuke or ion cannon strike on the enemy base, If the time runs out and the enemy hasn't stopped the countdown by killing your powerplant you win the game.
If both teams have fully upgraded and their powerplants are both destroyed. Then the only thing left is to slug it out until the end.