I guess one of the reasons they won't do it is because of the hassle/cost of reissuing membership cards which have expiry dates on them.
IMO CX only need to do two things to make MPO competitive:
1. Make permanent the elite tier bonuses which they had as a promotion for Sept 2001 to Mar 2002. I know this was only for flights on CX, not the whole of OneWorld, but I think I could live with that. (It was 25% for Silver, 50% for Gold and 100% for Diamond.)
2. Either reintroduce some sort of lifetime status, or do what KLM (used to?) do which is only deduct the number of Club points/miles needed to requalify at each renewal, not reset to zero.
Then everything would be fine.