Just because someone is no longer active or as active as they used to be, doesn't mean their previous posts or contributions should be devalued. We certainly shouldn't be looking to punish older members who took a big risk on bitcoin in its early days. Given that there have been 433 days since the introduction of the merit system, under your proposal, a member gaining maximum activity would have to have gained 216 merits just to break even, let alone thinking about ranking up. According to https://bpip.org/report.aspx?r=mostmerited, there are only 226 members who have achieved this. The purpose of merit was to stop shitposters being paid for shitposting - it wasn't meant to derank or limit the vast majority of members, which is what your proposal would do.

I still think the neatest solution is simply to change the requirement for a signature to earned merit. No one would be deranked, inactive legendaries would get to keep their legendary status, but shitposters who had their signature grandfathered in would no longer be able to get paid for their shitposting.