Have a different personal difficulty rule
Today the rule is the following:
PERSONAL_DIFF = MAX [ PoWMin ; PoWMin * FLOOR (percentRot * (1 + nbPreviousIssuers )/ (1 + nbBlocksSince)) ]
Which leads to difficulty curves like this:
Maybe we could have smoother curves, or be able to have only 1/3 of the members with the common difficulty instead of 2/3 like we can see in this graph (for percentRot = 0,9).