I understand where the resistance to diggers is coming from: you work hard to make a cool-looking place, and then something comes and ruins the way it looks because it affects the very landscape.
But this is Dwarf Fortress, and the community metagames and theorycrafts constantly to find ways to overcome challenges in Dwarf Fortress. Something as basic as a Cistern is something that people had to invent outside the game, but I'd venture to say a LOT of people make cisterns on freezing/scorching maps. Danger Rooms were developed by some clever people and the knowledge was spread everywhere, circumventing the perceived slow speed at training fighters.
When diggers are implemented, the first thing I expect is for people to build a big rectangular tunnel encompassing the entire level of your fortress. This way, they always break into the surrounding tunnel and get exposed (for your military to rush over and kill, or to fall onto weapon traps) before they dig through the next layer to get to the actual meat of your fortress.
These tunnels can definitely look aesthetically pleasing so long as they're symmetric and complimentary colors and what have you not.
Alternatively, people will build structures in underground caverns, in such a way that most of the fort is unreachable due to empty air between the cavernous walls and fort.