Occam's razor could lead to:

H, K, L, M, W, V: 100% EQM

G, Q, N, O, S: 50% EQM

or some variation thereof. Relatively minor changes required, establish tickets purchased by DD MM 2016 earn at one chart level, after at the new one.

Other "enhancements" could restrict "sticker" use, SWU applicability, etc. from that lower band of fares.

In the past, iirc, O class fares did not earn on certain flights, e.g. S. America?