well up to level 70 it shouldnt be too cruel on a player.
basically anyone can reach lvl 70.
if they "want to power level", so be it...at lvl 70 which everyone will reach,
they are the same.
the places where lvl 70+ can "train" would be PVP, dungepns etc.
in parties.
theres no real plans for any solo grounds above lvl 70.
lvl 70 to 80 will be like a small bonus.
their hp and mp get a little higher, and they get 3 stat points/lvl
(have a max_lvl and min_lvl variable. down and releveling wont work that way

)
also we will have a ****load range of items with different specialties
in the dungeons so people will often go there just to find stuff ^^
@ Knight Online:
All I ever did there was powerlevel...
The bosses were "just for fun"
no big loot or exp from them.... it was pointless... (Still, I killed the harpy queen with some buddys xD)
@ Pristontale:
A game also full of powerleveling, but in higher levels when it became a ****,
powerleveling looked different...
Nice parties in areas called "hellspawns"
basically, the mobs were "too many".
minimum 2 enemies per player, thus very good teamplay was needed
with area of effect attacks etc

god i miss those hellspawns, it never got boring...
exp shot up (and down if your team wasnt good enough, happened often)