Is your feature request related to a problem? Please describe.
It isn't.

Describe the solution you'd like
I believe it could be awesome if Dispensers and Droppers were able to place blocks like they are able to place shulkerboxes. This could be done with an IC (a Sign placed on the Dispenser/Dropper) but a more elegant solution would be a different way to toggle between block-placing and block-dropping mode. That way the Dispenser/Dropper could be moved around with a piston without the block placing mechanism being destroyed.

You could build automatic wall/floor builders and many amazing redstone creations. Combined with flying machines, elaborate redstone and pipe mechanisms you could event set up a system that might be able to build you a pipe storage system (without signs of course) in any size you want (really just depending, when you would stop the flying machine).

Describe alternatives you've considered
There really isn't one I have found.

Is there a reason you require a Dispenser for this? CraftBook has many systems that allow setting blocks based on the contents of containers.

I know about integrated circuit that are able to do this (place blocks), but I don't know of any way in which you could build a system that could also move while placing blocks. If that is possible then the suggestion really is void. I just couldn't find a way for that. I picked a Dispenser for cosmetic reasons, as that would be a rather obvious choice for placing blocks.