I would fix the thing where small objects or wedge-like shapes have zones bigger than the actual object, so you can't place bricks right next to them.
this is already possible? just the brick maker didnt bother to make it possible.
unless you mean 1x1 wedges
Importing processes made easier. So everyone has a chance to make something if they put their time into it.
Perhaps a custom in game tool that would allow you to create stuff on the spot and tinker with it until it's release ready.
blocklands already really easy to develop for compared to other games; half the time you dont even need to restart your server to test new code. the addon possibilities make a universal default tool to develop addons possible but very time consuming to make, and it probably wouldnt be better than the current situation where addonmakers model in blender/preferred modeling tool and code using a text editor of choice.
id improve lighting and efficiency of lighting; coming in at a very close second is brickcount