I am not sure that re-picking up placeables is the way to go. Perhaps for some, certain, challenging to place placables. Or maybe anything placed can be picked back up if it is done within like 30-60 seconds. That way you cannot make functional use of the placeable, and then move it again without a resource expenditure. If you are pulling something up within 30-60 seconds, it’s likely because you didn’t get it placed exactly where you wanted it.
It would be nice if you could paint, or adjust the wooden plan directions after they’ve been placed. Again - maybe an adjustment period is available immediately following the placing. I have gotten pretty frustrated with that one wall that at the last moment flipped outer face for inner face. If you could immediately radial these, and swap them around, that would be HUGE!
The map room is notoriously finicky to get placed correctly. Fortunately, this placeable can be picked back up.
But yes - relaxing the placement capsule for this object would be extremely welcome.
Painting would definitely be cool. It would be neat to see a little more variety with each of the block styles. Not every color under the sun, mind. But if there were some kind of craftable dye or paint (or rare dye loot item / ingredient… see this post about prized Abyssal foundation blocks), that would be very welcome. I would only counsel to not go overboard with this. For example, I would dig seeing a couple of different colors for T1 sandstone. Original flavor, and then perhaps two more. But I would be aghast if there were 20 different varieties of T1 sandstone.
The recommendation in the link for improvements for placables snapping-to foundations and player structures is a good idea. If this is considered - I hope it would not be implemented in an all or nothing method. Whatever is tweaked should allow for both free-form placement (current) and for placables to snap-to through some kind of a toggle.
I kinda like finding that dude who carelessly placed his furnace to where it clips through his exterior wall so that I can loot it. Just the same - if this was corrected, at least I would still have open windows. 
As another thought - if you make it so that recently placed structures can be picked up and replaced, this ought to be a somewhat reasonable workaround for someone who places a clipping placeable by accident, and then notices it. Strictly from a QoL perspective - the capsules on these common placeables that can clip walls should be identified and corrected.
I do like being able to stack storage chests on the top faces of some of the benches. To me, this is a benefitial way of staying organized… the chests on the armorer’s bench are obviously for leather, hides, etc. I hope that any adjustments that are made to placeables and overlap does not remove the ability to put chests on top of bench surfaces.
The higher the quality the hammer, absolutely there should be an additional benefit. Repair faster, or repair more efficiently, etc. If there is a repair tweak with the sieging pass to make repairing harder, the steel and star metal repair hammers might be a decent solution to combat raid-time-slowed repairing.
Placing some objects can sometimes be painful. However, I am not sure that I can think of anything to improve or optimize this. Except perhaps for making a pass on all of the large placables and their associated capsules to make sure that what is allowed matches relatively with their texture layers.
Larger foundation types. Hmm. I am not sure that I am a fan of this. I would prefer to have half-squares (triangles, Pythagorean hypotenuse distance structure nightmare for every other building piece) before getting larger foundation pieces. I see no need for larger pieces. Though - I suppose if there was a way to implement this that was a performance boon, I would be game for it. I don’t like the idea of a large swatch of my base getting bombed out because some raider was specifically targeting my Duplo foundations. 
The ability to set a placeable or structure preview would be huge. It would also be helpful if other players, or clanmates could see where you were trying to place to give you feedback on the placement. Both of these as features would be hugely beneficial. Having a click to preview, and then another click to set (think making a chess move, keeping your finger on the piece, seeing how it looks, and then removing your finger to set it) would be really cool. Whatever it is, though, hopefully it would be something that could be toggled so that it would not interfere with the player that just wants to quick-and-dirty place things quickly.
There are some very good ideas in this list. Thank you for engaging your players and seeking feedback! I look forward with what the team comes up with! 