The usual eight would still see use because they are already filing those slots, but what people took for the other four would produce variety. You won’t get the same extra four and while not an impressive range, it would mean different creatures faced.
Personally I don’t think this is a good idea. It defies the point of having a “cost” to swap boosts around. If people can just swap freely, it won’t generate sales because those who have them won’t spend money on boosts when they can just swap and will then just rely on free boosts for anything else.