Underwater City (And Submarine Vehicles)
Now we have all of these amazing aquatic cameras and mermaids, it'd be fantastic if someone could create some sprawling undersea cities... You remember seeing them in all those 'world of tomorrow'-type artistic renditions of the 1950s and 1960s! Great glass domes on the seabed, all interconnected by half-embedded pipes and tunnels.
Would have the bonus of doubling up as a prop for an off-world colony! An awful lot of planets out there won't yet have breathable atmospheres before getting converted, after all.
Alternatively, if a more realistic approach is desired, then purchase a cheap copy of 'Hidden In Plain Sight', by Richard Sauder, which has a wealth of actual US Navy plans for very real proposed undersea bases.
Similarly, I'd like to see some large-scale submarines, too. It's totally possible to convert spaceships for that role, but it'd be nice to see some oceanic behemoths out there; both military and scientific (the only real difference being the addition of open/close-able torpedo and missile silo hatches), although, I'd imagine that military versions might sell more.
Modern-day or futuristic styles.
Comments
For a futuristic one you might start with this & a suitable set of lights.
http://www.daz3d.com/sci-fi-city-kit
I did actually think of that one! The trouble with using that for underwater (or vacuums and non-breathable atomospheres) are the obvious sections of grass along the bases, though. ;)
Just remembered this one could do nicely!
http://www.daz3d.com/arctic-research-one
If you combine that with Ultrumarine, it would probably look pretty cool.