To comment on a couple of things there very much in brief:
I think in general having chunk borders drawn over two axis (rather than just horizontally as now) would greatly add to a feeling of size in the world. In moderation, obviously.
As for an area of a continent being 'city' across different times, I believe Environ is actually clusters of time and space randomly chucked together by some unknown force into the 'continents' we know today. So you're not just in a city split over different times, but in a region of bits of city, bits of forest, bits of mountain, etc. I do, however, absolutely love the idea of some day visiting the exact same region in different time zones. Clearly specific regions (as opposed to types) would need to become a lot more unique than they are now for anyone to even notice, mind you.
I believe, for reasons of maintaining the optional nature of hardcore areas (or rather, to remove any feeling from those who do not venture into those regions of missing out on something) there will never be anything in them which you can't otherwise acquire elsewhere - aside from, and this could be a lot of fun, things of a purely aesthetic nature. One suggestion I had was after spawning a lava escape mission using a new guardian power, a possible enchant with completely normal enchant effects but also guaranteed to leave a harmless trail of flames in your wake wherever you go.