you cant surpass the brick limit.
its a limitation that is very much hard coded into blockland's engine.
you can use certain hacks to exceed it, but it messes up your game, so ive heard.
oh yea, and the only way to get around the limit by "unrendering" would be to completely deconstruct and reconstruct the island, thus temporary lowering the brick count, it can be done, but it would be waaay to much work and, as for a multiplayer standpoint, probably not a good idea.
gsf's terrain generator does something similar pretty efficiently, but uses an algorithm to construct randomized land, and sadly doesn't generate anything extremely detailed on its own without players building it themselves, you might be able to use code from it to get the desired effect, although, again, in a multiplayer game this still wouldn't work, as multiple players could cause blockland to build more then 256,000 bricks.