If they learn from WOW, and other MMOs, I think gaming in general will start to do things right.
Burning Crusade in WOW was pretty much perfect as far as difficulty goes. I played with 3 different guilds. One somewhat raid oriented, but not super hardcoe, with some casual. It took us a few months to clear Kara, and other starting raids. I love progression, and moved to a different guild and pressed hard to clear through Black Temple when it was patched in.
I think the balance should be that the end game content should be available to any **competent** player, and I think in Burning Crusade that was fairly true. Sunwell was a little extreme, but we had some members who ranked as "just competent" ... those that know not to stand in fire, and could build a decent character ... and we did pretty damn well. The 3rd guild was Drow - Top 5 US continually... we just smashed through [censored].
If they make it like Lich King, where a pug can clear all the content... [censored] that. I don't want "hard mode" I want the content to be legitimately hard. Niche encounters that have scaled difficulty, like Sarth 3D - great hardmode option, but pressing the "make this raid harder" button isn't the way to do it.
I want legitimately hard content. If you want to see the end content, work your ass off and go see it, nothing's stopping you. If you want it handed to you, and don't want to work for it, [censored] you, go play Hello Kitty Island Adventure.