A major flaw I see is that this will basically be like a cheap, enormous donor vault. People will just shove all of their items into their plot and boom, this becomes like a creative server with optional "hardcore".
I suggest either making the world pure creative and disallowing the transfer of items OR disallowing the transfer of items but still requiring people to gather their own resources, with the world being a normal nonsuperflat world.
I vote for the second option. Personally, I don't like the look of superflat worlds. I think natural worlds are much nicer, and 99% of my structures I try to integrate with naturally occurring features. Since item transfer would be off, people could still mine for resources and even sell them for coin, but they wouldn't be valuable in the same way that they would be in Bastion; blocks would most likely be priced according to their aesthetic/practical values.
Still, I think my main point is that if items can transfer between worlds, there shouldn't be a way to safely store them other than LWC. If plots are protected, people will use them as alternatives to donor residences. I guess if they're priced the same it wouldn't really matter, but then people could potentially have 3 or more protected areas to store things, PLUS their town if they're in one.
So again I vote for the naturally generated world with item transferring disabled.
Sorry for all the rambling, hah.