Here are my thoughts:
One of the main purposes of land is to give older sets a place to retire, generating a deflationary effect on card supply and helping old assets hold value.
So, why allow the current editions to work land at all?
My suggestion would be to have it so any card/set that can still be bought in-store (Riftwatchers, Gladius) or earned from battling (current soulbound reward set) is excluded from land work completely. Or alternatively have a hefty efficiency penalty until it is out of print. This is a much simpler, straight forward system that fits better with the goals land is meant to achieve.
sorry but the ``main purpose'' has not been true for a long time. with the pp cap which was introduced you can reach the pp cap with untamed cards so alpha and beta cards have become pretty useless for land.....