Start with a set number of innings. I'd say 2000. Only Dizzy Dean would be the primarily SP to be removed. Gossage/Sutter are out, Paige is out, Ruth and O'Day are out as pitchers. Of course, Gossage/Sutter are RP. Have to decide if they're HOF pitchers as RP. Paige, of course, was Negro League. Ruth isn't in as a pitcher. O'Day was an umpire(I think).
But, from this day forward, if you didn't pitch 2000 IP, you're not eligible as a SP. Special circumstances(meaning RP).
So, to me, Dean, Gossage and Sutter have to pay to visit the HOF from now on.