And you are all basing this as if we'll be waiting another 5-10 months before we get the next cap and thus dictates that the xp required to the final cap to be large. That's absurd. The 21 cap only needed a third of the xp requirement that we have now and I enjoyed that one way more than what we have now.
Large xp requirements doesn't make anyone more interested in the game. Grinding doesn't keep people interested in the game.
What'll keep people further interested in the game is content not an obscenely long grind. How do you think PL has been alive for soon long? Content. Tell me all of the sets and items that farmers can spend time hunting for. Tell me how successful the 50 cap was and why. The answer is content and not an absurd amount of grinding.
What we need is more content as in side dungeons, special items to farm in then (forbidden tomb xaxis helm), and just more things to do then level up five to six times and be done with the game.