I don't know what to call this, a theory, an idea, or a possible future bug ,but since the build height is confirmed to be raised in 1.17 snapshot and even higher with data packs pushing it to 2048 and CC 1.17 fabric's plans to push it higher, can you keep the stacked dimension stuff but put it where the player specifies and assume at least the computer limit of build height (which is (- and +) 1.07x10^9 or (- and +) 1073745663) this is the number which is possible to build at in cubic chunks 1.12.2 and 1.17 snapshot of it. The thing is that without assuming the world height and giving player control to determine where to bottom and top of the dimension is from 0 - 256 to (- and +) 1073745663 first being the bottom number and second is the top. One last thing about this possible config build height option thing please don't make it a slider and make it an input box for numbers. :)
that and I imagine if the build height is not assumed in the future it will break with a lot of mods :/

I closed this because I know it isn't an issue :) as it said in the title :)