Making drawbridges more complicated kind of falls under the machine improvements list, along with multi-tile, spring-driven weapon traps. Rope ladders are already slated for development and have been for a while - iirc the reason you can currently build staircases from above as well as below is as a placeholder because Toady couldn't get ropeladders working properly yet.
The rest of it will probably come in with the hauling improvements, along with minecarts and the like. Right now it's not as useful as, say, a well, because dwarves can happily carry gold-studded lead doors down a 30-level spiral staircase.
Now, when it becomes useful I'm all in favour of it, along with capstans, winches, etc.
In fact, one thing I'd absolutely adore would be aerial ropeways, since low-tech magazine says they've been around for a long time - see
http://www.lowtechmagazine.com/2011/01/aerial-ropeways-automatic-cargo-transport.html. tl:dr version: think like a ski-lift, only for stuff, and with way more potential for FUN.