What it was: A sequel TV series. This series would've followed the now older (and thicker) crew of the USS Enterprise on an new mission into the unknown, along with a bunch of young new characters. They would've included Xon, a young Vulcan science officer (needed because Leonard Nimoy wouldn't sign on to the new series), first officer William "Will" Decker and Deltan empath Lt. Ilia. In addition to appealing to a younger (i.e. not middle-aged) demographic, the younger actors would've given the production more of a chance to continue if the original cast ever decided to leave.
The series never got made because the TV network died, but the new characters were used for the first Star Trek film, and some of the episode plots were later recycled for the series Star Trek: The Next Generation. Read about the other projects at blastr. Link -via @johncfarrier