Let's be serious.
An adventure mode like this would be really cool but there is one massive problem.
The engine
This has been said time and time again that the engine that blockland uses is extremely outdated and the game would need to be ported to a new engine. And there is problems with that to. The game would most likely have to be rebuilt from the ground up, and that would take a lot of time and money. Then there is compatibility with addons and saves. If the game was ported and the old version is still up that would split the entire playerbase. Then again there is the problem of who is going to port it. Badspot doing it is very unlikely, there would be a chance of badspot hiring someone or a team to port it, which is still unlikely. Lastly there is the community doing it, which is the most likely of happening.
Just some thoughts.