I think it would be in the interest of many L4D VS communities if there was a plugin which ensured fairness in a Versus game.
What do I mean by "fairness?" Anything really to make the match more fair. For starters, the second team should get a tank if the first team got one (per stage). The second team should get T2 weapons before a tank, if the first team got T2 weapons before a tank. Both teams should have the same amount of medkits and painkillers. Perhaps even make all the item spawns completely the same for the second team.
To avoid a situation where the second team would know the exact placements of everything and thus the second team would always have an advantage, swap teams every map while retaining the scores. This last part by itself would be alone an excellent component of a fairness plugin.