I think it's a silly idea to think the WHOLE ENTIRE FRANCHISE will be 'diluted' or somehow messed up by a new series if it's a flop. New material can only enrich the universe.
There are tons of possible angles to explore the star trek universe. Things like, what's going on on Earth, a show set in the academy, or what people do all day in a world where they don't need money. Not everyone works in space do they?
Maybe follow a colony. Maybe follow an alien colony. An alien ship? Enemies of the Federation?
The 25th century, when they finally leave the galaxy?