This map shows the potential of what could theoretically be added to the game once we have wrapped up classic progression:
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There are quite a few zones that they were able to stuff into the original three continents.
So if you take out all of Discord, Taelosia, Luclin, the instanced LDON stuff, The Planes of Knowledge/Tranquility, and anything else meant for level 65+ there is still a lot to work with.
I would also remove anything that isn't mentioned in some way shape or form in classic lore. So if it involves a storyline that's post Luclin then it shouldn't ever be included.
Being able to use the zone in locations from these other expansions can give way to many options...
I know this is all just hypothetical talk... but it's still fun!