Sending Space Probes to any of the Planets takes way too long. I would like to see an in depth story comparing possible new space propulsion technologies. How much mass could be sent to a planet in how much time using each new propulsion technology compared to existing rockets?
New propulsion technologies could include Variable Specific Impulse Magnetoplasma Rockets (VASIMR), Ion propulsion, Solar Sailing, etc.
With the advent of Cubsats it seems to me that one of these very low mass spacecraft could be sent on a planetary trajectory using ion engines or solar sailing. Larger spacecraft could use VASIMR.
I think an in depth story on future possible propulsion technologies would be interesting to Astronomy readers.