First of all, where have you been all my life? To me, this is the best dungeon editor I've ever seen, hands down: All the features I really need while at the same time not overly complicated to use, and requiring little to no post-processing to get exactly the aesthetics I want. Kudos!

However, it doesn't yet have all the features I'd like, so here's a couple of ideas for further improvement:

• We need genuine lines. The line macro tool is of no use with layers that use dashed lines, as it seems to actually create a line that folds back on itself, and it's a matter of luck whether the dashes of the "forward stroke"  coincide with those of the "backward stroke".
• Speaking of lines, a curved mode would occasionally come in handy there, too, akin to what you're doing with the path tool.
• I'd like to see additional door styles, most notably something that works to indicate a grating door (is that a word? I guess you know what I mean); some ideas: (a) a simple line with automatic gaps at either end to distinguish it from a wall, (b) a line with short perpendicular strokes through it, (c) just a series of dashes perpendicular to the door, or (d) a series of dots (or short dashes) in line with the door. (While the latter could be achieved with a simple line in a dashed layer, even if that worked properly it would feel cleaner to have such door markers in the same layer as other doors.)
• Speaking of doors, I frequently use double doors. It would be neat to have a switch to do them automagically. (For some reason, drawing doors tends to take some time; or maybe that's just my dungeon becoming excessively large?)
• More features for the text tool, please. Most notably, I'd like to see a preset for the font size, so that I don't have to manually resize each text element to the desired size. When there's a lot of text to add to a dungeon, this would make life so much easier.
• Also, please make it so that text elements also snap to their left or right, to more easily align multiple lines of text.
• I'd love to see more options for stairs, most notably (1) support for curved stairs, and (2) an alternative style that works reasonably nicely be used to indicate ramps (my suggestion: two lines forming a chevron), which of course also needs to come in a curved variant.
• Please add a switch to the polygon tool that toggles between the current "distance to corner" mode and a new "distance to edge" mode, so that we can more easily create e.g. octagonal rooms with an exact distance between walls.

(Also, have you ever thought of implementing a mechanism by which we could use compass-and-ruler-ish construction to define helper lines (and circles and points) to which the cursor could snap? Maybe as a special type of layer?)