Doing the same dungeon on 10 and 25 every week on multiple alts is boring and time consuming. That's why I abandoned 2 of my alts... Can't raid every day of the week, I still have work to be done. If they manage to balance well the difficulties, this will be a great improvement. You can do only 10 man version and feel you achieved something.
Also, only 2 tier levels (reg and heroic) per content patch, this means stats will scale slowly and we won't over gear heroic dungeons so quickly (aka turning them into boring daily runs).
I'm looking forward this change! Looks awesome.