The Edit Block is a block that, when placed, slightly tints all blocks within a 16x16x16 cube such that the Edit Block itself represents the front, bottom left corner block (Alternatively, just the corner blocks could be tinted). When clicked, the Edit block displays an inventory section (like a chest) and a few buttons labeled "Map", "Build", and "Clear" and a text window allowing the block to be given a name. When "Map" is selected, the Edit Block changes color to indicate that it is storing a block pattern. The Edit Block also has a light to indicate if it has the necessary inventory to "Build" the stored pattern and that there are no existing blocks in the way. One can simply use this block to store constructions and copy them to new locations. Of course, the inventory needs to be replaced whenever the "Build" function is activated. Different Edit Blocks could store different patterns, and the inventory could be filled using hoppers and the build function activated using a redstone charge for some very interesting redstone contraption possibilities.
With an Edit Block (just a working name) one could carry around a portable house or redstone contraption or build larger structures with less repetition. One could have a collection of redstone circuits ready to go. One could even build something to push these blocks around, refill them, and activate them. I've also considered an option for deconstructing a structure if it matches exactly what it has mapped, rather like the way dispensers suck lava back in. To accomplish this, a "Deconstruct" button may be added to the activation menu. This would be the default action if the block is activated by redstone while the inventory is completely empty and the bounded block pattern is a match. Edit Blocks can be emptied using hoppers and can be added to minecarts.
The Edit Block does not map empty blocks, so will place blocks around existing blocks if they are not in the way.