Clearly it has been the imagination of development that has added value to domains. So, I have to hand it CTC for thinking.
Sample popular POSITIVE cash flow uses of sub-domains are:
City sub-domains &
E-mail sub-domains
(That is my short list of the first 100 uses. I realize that may be 50 posts saying I forgot about sub-sports or sub-perversions. )
However, Newyork.Exploration.info probably will not work easily and Blackplague.exploration.info is worst.
As far as your idea, my gut is that it makes more sense to have a home page broken into areas as SPACE, AIR, LAND, SEA, & DOMAIN ââ¬â the visitor clicks on the area of interest.
So, as a sub-domain ââ¬â I do not see added value more than is possible with any domain [eg. space.dnforum.com] unless you can elaborate (develop) further.
Good luck