The only issue I've got with props (and builds actually) is how to load them into the game. In an ideal situation you'd be able to hit the "load" button on the in-game save browser and it'd equip your player with a special brick which would be a square with the exact dimensions of the build you're trying to load to make it a bit easier to position and everything. Obviously that's not possible at the moment but I might pitch the idea to Badspot and see how keen he is on adding some kind of system to do that. If anyone else has got some ideas about how to place builds you're loading when you're not exactly sure about it's dimensions then definitely discuss them in this thread.
What what is wrong with just downloading a .bls file and loading it duplicator style?
Or duplorcator style too.
Unless this is something that is being handled completely client sided...
I worked out duplication saving/loading in buildbot if using that or something similar is acceptable to you.
Or you could even make it create a macro, although buildbot is sorta the same thing, except faster.
Heck, I could probably put together some basic client sided prop downloading and loading pretty quick if I can get a server to host the stuff.