as i understood, you can only access the new content with a new char in a new realm. previous chars and realms will stay as “legacy” realms, but u can’t take things over from there.
which also in some cases might not work or might not make sense anyways since several systems, like for example the enchantments will get a complete rework.
i somehow seem to recollect something floating around about increasing the lvl cap, but i am not 100% sure if or when that is happening. so please don’t sue me lol
you can check for all news we got on discord and other channels additionally to the breach showcase here: Updates and discussions from the official Discord
…including screenshots, animations etc. but be warned, its a lot! lol
and thx for keeping your questions “in an orderly manner” 
always appreciated!