Whoa! 2013?! 2 years of a 50 cap (even if most content is added - which it will be in that time period) will just mean most people walking around with multiple Rank 50 jobs (even if they didn't want to level them - because they can't go any further with the class they wanted to play).
As long as Yoshi-P and the Dev's remember that there will still be plenty of people at lower levels when they raise a level cap, and continue to make lower level content (as well as higher level content), there will be plenty to do. In fact, I would have thought that if the lower level stuff is quite good, it might even encourage some players to go level a new class.
Regarding the OP, yes, I would like to see a harder grind for any future rise in the level cap. Currently 1-20 is ridiculously easy (I'd like to think I'm a casual player - I play 1-2 hours a weekday evening if I can get on, and maybe a little more on the weekends if I can get on - and obviously I regularly can't get on), 20-40 is still not a chore, and I've only felt 40-50 is being time consuming (i've only reached Rank 47 on my main class so far). I would love to see the difficulty curve continue for further levels, and hope SE don't go and nerf this in a few years (as they did in FFXI) when people get lazy and can't be bothered to make the effort anymore (which is a slap in the face to all those other players in the preceding years that ground their way to the top).
Even though I'm a casual player (though I would like to play more), I've managed to level fairly well as my fellow LS members group together to do leves every reset, ensuring good SP (despite surplus - which even I find annoying as it cripples your attempt at efficient levelling in your short playing time). Those LS members that have more time have levelled 2-3 classes in the same time (i.e. they outlevelled me a few times and I had to wait for the lower classes to catch me up so I could join them again).
Sensible casual players need to accept (and I think most do - there's just a minority that whines) that they cannot fly up the levels and obtain endgame/higher gear as fast as those harder-core (couldn't think of a better word, lol) players that put in way more hours than they do. But (at least to me), the achievement you feel when you get there is no less awesome because you know you've done the same thing.
I agree that if you're going to consistently play solo (because it's "too much effort" to play with others or join LS's?) then you will find it hard to level up. But then I also feel that if you're that kind of person, wth are you doing in a MMORPG? You might as well go play an offline RPG.
Bottom line: If it takes me a year to get from 50-60 (if/when they raise cap) because it's hard to do for the casual player, I don't care. I'll do it, and I'll feel like I've achieved something when I get there.