Yea, supcom really does not lend itself toward creating artificial terrain like cities and other structures. imo all the maps that have tried this look at best acceptable. It's just not worth it, and sticking to natural terrain leads to much more satisfying results.
If on the other hand the editor could be expanded by a whole bunch of new props, similar to the large wall segments... as well as more tech-themed decals... but we would need somebody interested in creating that theme set and then it would need to get patched into everybody's game etc...
Though there are certain limitations that probably cannot ever be overcome. We will never have actual bridges for example, which is a shame. Another thing that is not possible for the same reason is platform-like structures that extend over a cliff and the like. One of the few things supcom2 did better... Bu tthen again, I really don't like all the tech-themed maps of supcom2, so maybe it's better this way