I like the sound of the changes as well, indeed distinguishing the ocean and ocean shallows more is something I had considered suggesting above.
This is all a little off topic but...
For the oceans....and this could be unnecessarily complicated to do but and is just something that popped into my head, how about making them deep rather than wide, as in, for the first chunk you enter from the sides as normal, but all the entrances to the others chunks are down rather than left\right, with the only real ground the ocean floor at the end of the region, however deep that maybe.
So essentially the region would just be you plummeting down to the ocean floor far below, maybe make it really variable how deep it goes, and tie the risk\reward in to it so you could just end up with 3 chunks and not find anything, or i could get "lucky" and get 7+ chunks and end up having to fight, well some boss monster that lives in giant ocean trenches for an arcane ingredient.
All the rest of that sounds good, but this little parenthetical statement just got me thinking, if we have land from every age, we should have water from every age right? Frozen ice age oceans, underwater future robot city oceans, steaming oceans with lava bubbling up from whatever age the lava flats are in, etc. And were there any ages that didn't have acid for water? If not, how exactly does the biology of the average resident of Environ work? I mean, how are the plants even growing?
I know, I know, post-1.0 stuff. But it sounds fun.
Again with the, Obviously post 1.0 disclaimer, but one of the suggestions i made somewhere around here was that this sort of logic should apply to all the areas, e.g. so the map gen says "this area of the continent was a city" and then have it cut up in time, so you might have a region from when the city was a tiny village, or one from when it was a thriving metropolis and then one of it falling into ruin. For the forests and the like it would be increasing levels of environmental destruction and industrialization.
3. Don't put anything that is required in the oceans, but let those be another one of those "optional but incredibly difficult" sorts of areas that people like to have.
Picking on the "required" bit, the real question to my mind, and this applies to other "hardcore" areas is, will there ever be specific rewards for these areas? something special to make it worth the effort. Things that leap to mind.....
1) Special arcane ingredients for Special spells. (basically an arcane ingredient that is used only in the specific spell(s) so that it doesn't interfere with anything else)
2) Easier access to arcane ingredients.
3) Special Items
Now obviously there are problems with these, the issue with 1) is no matter what spells you use, personally I was thinking non-direct damage spells of some sort, unless they are balanced perfectly, people will feel obliged to do struggle through the areas. because people are like that.
The same sort of things apply to 3), it would have to be of such utility (either very specific or horribly general) that people don't feel like they Have to have it.
2) is probably the one with least upfront issues, it makes rummaging through the hardcore areas a sort of implicit secret mission. I was thinking of things like rare rooms with magma\deep magma in the deeper lava flat caves, or sea essence for the oceans.