That's a great idea. But I didn't find any docs that explain how to override DND. I opened a feature request instead, so we'll see how it goes :)
If you start overriding DND, now the user is going to want super-DND. Which somebody will then want to override, and so on. The correct solution is that your users need to not set DND when they in fact need to be disturbed, and your systems shouldn't be disturbing unnecessarily, and to the extent that's a really hard problem, well, yes, it very much is, but an unboundedly-large hierarchy of "bother that person, no don't bother me, SUPER bother that person, no SUPER don't bother me, SUPER MEGA bother that person" isn't part of the solution set.
This caused more than a few missed announcements and made escalation hard for a bit.