Yup, it is by no means a priority. There's Hinin's tweaks that implements a still good version of this change, but making the polder destroyable would truly make it a strategic asset as well. Maybe someone can propose this change next month with more insight if the AI can use/not poop itself over this change?
What I'm saying is that if it requires changes to unit movement and/or tactical AI and you're unwilling to do it, they're kind of up a creek without a paddle, since you're by far the most knowledgeable on this code.
Just dropping by to say: if we have to break the game for a whole month because this change, by all means don't!
There's always next month, and in the meantime you could evaluate if it's doable without too many sacrifices or breaking the game.
(Sponsors have indicated that they are able and willing to perform the code changes required for this proposal if the community votes Aye on it. Other coders are free to sponsor this as well. A proposal without a sponsor will not advance to the Voting Phase.)