Not sure if it has been mentioned, but I think a cool option would be a mirror option. For example, you can already make a base, group it, and rotate 180 degrees to make a copy on the other side of the map, but, depending on the symmetry you want, it might end up being backwards. Mirror option could basically be a vertical plane that will copy the blocks on one side to the other side, being the exact same length difference to the plane. For example, place the plane at position 0 and put a block 2 units away from the plain. that same block will also be placed -2 units from the plane with the mirrored rotation as well. you do not even have to build a symmetrical map with this, as it could be applied to building structures as well. Build half the structure how you want it, and Bam, its done.
I would like to see an adjustable and/or smart canvas boundary, to allow for larger maps. Essentially do away with hard limits on map size, or at least raise the upper limit. The ability to go as high as 10,000 or more would be nice for epic large maps (especially if we can use AI to basically make campaign maps).
I'd like to see more musical notes in the scripting. Maybe even different instruments to choose from. Some type of decay or reverb option would also be nice (especially if it could be set to a variable).