I am glad to here Slabs and ramps on sides will be implemented, so I got a few more for you.
Cylinders & Half-Cylinders Horizontal Placement - too many uses to count
Flat 3/4 Ramp Corner - The inverse of the small 1/4 ramp corner // Like the 3/4 ramp corner but no center crease - My roads on 45 degree lines would appreciate being able to change heights.
Pickaxe Right Click - Small terrain removal - Sometimes landscaping feels like trying to paint the trim on a house with a fire hose. Would it be possible to use right click on terrain to remove a single/small piece of dirt/stone?
Chalk or Chalk Line dispenser - A tool to place temporary lines so I can line up parts of my project with each other, then right click with tool to remove.
Half Height doors - Ideally for saloon doors, two part doors, fence gates, and one you can place a poster on to hide your safe behind it.
horizontal and slanted doors - for basement/cellar doors, half height ones = trap door/hatches
Here are a smattering of items to consider
Wooden Poles/Metal Pipes/tree trunks - cylinders of various materials - I wanted to build a log cabin...
Stone/Wooden Arches(half and full arches) - So many uses so needed full range of placement options of a construction item, and I would like to be able to pass under through my aqueducts when water is implemented. I know it will be difficult.
Free Hanging Wires - For when you implemented electricity, I can run power lines to all the buildings, tesla coils, and jacob's ladders i expect to have. Also to hang lights on, signs, and decorations.
Boulders/stones - for rock gardens and free form path markers, could even spawn some of these naturally in certain biomes
Shrubbery - So I can put in a couple to form a nice two layer effect and...
individual bricks/flagstones - for a path through my shrubberies.