[FONT=Arial]The way that ranks work, especially in PVP situations or places that are competitive don't have a lot of leeway. We have had ranks in Kit that donators were allowed in the past, but they were removed as they breached Minecraft's EULA policy, which roughly states that donators are not allowed to be given anything that enhances game-play and gives them the edge. According to the EULA the only thing donators are allowed to receive are aesthetic perks such as the /hat, /effect, /dis and various other commands that we already have. For this reason re implementing ranks into kit that donators have access to without earning them in game is breaching Mojang's EULA policy and is technically illegal. Although it is true if you do some research that as of yet Mojang has not punished anyone for breaching the policy it is still illegal none the less.
I think the part about turning in your kills to buy ranks in-game is a really good idea though, and maybe even a prestige system could be implemented where you can prestige, resetting your kills and deaths and giving you a special kit. The only problem I see is that you cannot access these ranks by donating with real world money, they would have to be solely obtained by in-game means. I found it slightly hard to understand what you were saying, so I'm sorry if this is exactly what you meant, just thought I would point it out.[/FONT]