I know for sure that before 2.0 released Yoshi said they plan to open up the dungeons for less than 4 players at some point in the future.
I don't know if that notion has been abandoned or not.
At the very least, being able to go into the instance solo and call out my chocobo etc to farm drops would be a step up,
but...
A true open access area would offer more gameplay opportunity while putting less stress on the instance servers.
And as others have mentioned, the amount of work shouldn't be too heavy.
They could just take the existing skin, and heck, even the monsters for the most part and people would be happy.
The tweaking would be in the form of mining, harvesting, fishing, quests, drops etc.
Much less effort than building an entire zone.
