I want to make a game mode similar to zombies, where both the red and blue team are armed. Whena a red guy kills a blue, he converts him to red, and vice versa. Can it be done, would you play it?

Seems good but if I were you, I would add in king of the hill like objectives to spice up gameplay. I think what you're doing can be done though considering the fact that there is that zombies/infection gametype that I see a lot. If I remember correctly, kirby made an invasion gametype.