an awesome addition to the game would be putting a decap prize on a single player

There are player-held bounties floating around in a sub forum somewhere on here...forgot where

A decapprize in singleplayer? You can't just get tc from getting a decap in sp because that is super easy and will be used to farm tc. In mp there already is a decapprize that players can use.

Last time I used the decap prize in my server it ended up not giving tc to anybody

that would be too easy in single player,
you can use mods or change gamerules to decap people easily