I don't think it's about XPM replacing YAC, but I think there's mainly 2 things that are putting in danger YAC and preventing its raise:

- The sudden, N increases. I don't know if it's possible to 'smoothen' the effects without a hard-fork, but it would be worth considering. The average foe is probably not OK with their hashrate halving overnight and difficulty taking 5-6 days to adjust. Since the N concept probably has to stay this way as it's 'the concept' of the coin, I guess the change should come with difficulty reacting faster after a N change.

- The lack of development news (not blaming the dev(s), I understand you can't do miracles with few numbers, but it's an issue from outside).

If these 2 things are tackled I don't see why YAC couldn't become more widespread. If nothing changes, well, I'm afraid we'll all have a good amount of very cheap coins.