1) It maybe would look strange between the existing maps, because of the different look.
We have to start sometime. Our maps don't really have a unified look anyway, so I don't consider this a major problem.
2) It would need at least some new models (vehicles, furniture).
We do have some existing models that look a bit futuristic. I can think of at least a motorcycle... Furniture could be created in UFORadiant rather than models (models don't share the same lighting, so I try to avoid them when possible).
But you're right. Some new art assets are probably going to be required, so it will be a bit more work. Same with the UFOCarrier. The UFO or alien base textures are probably not going to be enough. That said, I may be able to help with some new textures for your if you have a need you can fill from FOSS resources out there.