Terrain & interiors have to stay. What kind of crap idea is it to eliminate 90% of the modding community for a purely aesthetic feature that most kids with netbooks won't even be able to use.
This all the loving way.
To add onto my minirant earlier, interiors is what originally defined Blockland. Other games don't provide a unique environment for every artist. New artists might hesitate to build too, as now they're forced to build things from scratch. This probably will put off new builders, people who could hone their artistic skill through practice. A white expanse to work in isn't very encouraging when there's nothing to base your ideas off of.
Interiors and terrain maps provide a solid ground for new builders to start. Who hasn't thought of ski lifts on slopes? "Toy" builds in Bedroom? Food builds in kitchen? When you give people an empty slate, you literally force them to create their own foundation, and many who don't enjoy this art form won't be able to do so.
Another problem with having slate-only maps is that it encourages build stealing. When new people don't have a foundation to build off of, they try to find one, which usually results in stolen builds that are "rebuilt" from scratch. This reduces creativity and just leads to filling this community with more unoriginal builders.
However, I'm not completely against this. Having a forced empty slate also roots out nondedicated people and improves the community overall. If any of you have played the game FreeAllegiance, you would understand. That game has such a high learning curve (beyond dwarf fortress) that newbies tend to drop out quickly, leaving only the mature people who truly enjoy the game.