(Mercenary Proofreader strongly dislikes the term nanite — he prefers nanobot, if only because critter will probably never catch on as a slang term for ultra-tiny robots, particularly those used for medical or other bio-related purposes — but he is willing to tolerate it when someone is paying him. 🙂 )
Supersoldier ought to be one word. Yes, even though WordPress’ spell checker is red-squiggling it. (For the record, though, WordPress’ spell checker is red-squiggling nanite but not nanobot.) That particular glitch isn’t a big deal, though; leave it as two words if you want.
On the other hand, the example sentence is compound, which means… Class? Anyone? Right: it requires a comma before the conjunction.
It is the year 20XX. England is inhabited by nanite-enhanced supersoldiers, and artistic expression is punishable by death.
The XX just means the creator of the writing prompt didn’t want to be too specific about the year; insert whatever two digits seem appropriate, or just don’t worry about it.