Well, for the time being you could hook it up with the spawn protection thing. /pos1 then you break north-west block, /pos2 and break south-east. Then /set <block> to simply replace all blocks with that block in the area?
That'd be a nice place to start, then just add the other functions as you can. If you could make this, it would be amazing on Terraria, I really hope you can do it!