otoh, all showing the amount to marshal will do is have 2 people with lots of time clicking links every few minutes do so instead of 1.
nothing wrong with that, of course, but fundamentally far easier to just allow a custom warning threshold to b set, so the game blast out a message rather than having people look and send message. even if you do that, there's nothing stopping you from showing the amount to the marshal as well.
the tax thing... if it's done, then it would make more sense to take the cut from gold in hand. taking from the bonds part of taxes or even directly from the region would mean you can park an army in allied city and be able to fund your repairs using less gold in hand. ie... magical bonds->gold machine.