It’s a very interesting observation overall that both high contrast and low contrast can be good for accessibility.
We could consider our current symbolic icons a part of a “low contrast” mode, and give them some subtle color for a new “default contrast” mode. This could could be done via internal CSS, so it just turns on and off, no need to swap out a different icon theme. A high contrast mode would probably involve a whole different icon theme and dispense with the symbolic icons entirely in favor of full-color ones — which would of course need to be created and maintained, and that adds some risk. In the meantime, the new default contrast icons with a little but of color would have to suffice.