How about anyone retiring in the next three years gets 100% of the benefit they now expect to receive, then the fraction is pro-rated down over the next forty years (i.e., retire 4 years from now & get 97.5%; five, 95%, etc., down to 39 years, 2.5%).
BTW, this would encourage more retirements in the next few years, creating more job openings.
Not a bad idea....