Few more ideas
Russell’s paradox An achievement achieved by achieving all the available achievements.
Singin’ in the rain Making a bard go outdoors while it’s raining.
Much blowe For one hit killing a dog. Shiba would do best, but I guess there weren’t any in Europe back then.
Burning the bridges Awarded for attempting to burn a bridge. Obviously bridges in the game are going to be indestructible, players should be compensated for trying.
Hacking on the threads For attempting to destroy a bridge with the sword.
Blast in the past Firing at the bridge during the final castle siege.
Disassembly For trying to use some construction tool on the bridge. Crowbar and so on.
Ants marching For managing to maneuver guards into marching over the bridge.
Stress test The player puts at least five horse carriages on the bridge at the same time. (Because proof load testing of bridges is often done with military tanks.)
You’re gonna go far Meta achievement, for attempting at least 3 different ways of breaking the bridge.
X bridges of KCD where X is the actual number of bridges in the game, for completing an Eulerian trail over all of them.
Bridge troll For blocking a bridge so that an NPC could not pass.
Jim Bridger For being pursued by a large number of enemies and killed.
Crossed a bridge for crossing a bridge when you came to it.
Then there should be an achievement for managing to avoid getting any achievement for at least 10 minutes into the game.
Merge the quest system with the achievement system
Every quest has an achievement tracking it across playthroughs and every achievement is a quest of sorts, its completion will grant XP or count towards improving some in-game skill. For subsequent playthroughs player would have the option to have these bonuses applied to their new character as well.
Making achievements moddable
The game would support a number of triggers that the achievement mod could register for. There needs to be a system of public voting on achievements to weed off the interesting ones. Using triggers would guarantee that achievement tracking is lightweight on system resources. That way the game can track progress on almost all submitted achievement mods, maybe even before the player opts in, as if all were installed at the same time.
Just a crazy idea. Since Steam Workshop does not support it and probably never will, it would require some custom infrastructure.