I think a really simple fix for the persistent item being able to cause in game lag is to set a maximum entity limit. You can either make the max entity by entity type or for all items and then set a despawn priority.
Basically, if the priority is Diamond Weapon, Diamond Pickaxe, and then dirt and you had 16 Swords, 12 Pickaxes, and 490 dirt blocks with a server set to max 250 entities then once processed you would still have 16 Swords, 12 Pickaxes, and 222 dirt blocks. This is easy(maybe not in code as I don't know how easy it is to count total entities), minimizes litter, and reduces need for admins to get involved while still protecting valuable items people care about since the highest priority items are unlikely to build up as others are sure to collect them.
It also reduces the possible exploit of using this to grief a server when there are no admins. If I find an easy item is set to not despawn, say wheat, then I just drop 4000 of these away from each other so they don't stack. This causes thousands of entities to linger on the server and makes everyone's life miserable.
Good mod and I might use it once I get a forge server up and running.