Star Trek: 10 Things You Didn't Know About Lt. Barclay
3. Barclay Was Almost In TNG's Lower Decks
Reg Barclay would be such a great guest star for an episode of Star Trek: Lower Decks that it's surprising that it's not happened yet. However, Barclay did almost feature in the Next Generation episode which inspired Mike McMahan's animated Star Trek comedy. Lower Decks was a well-regarded episode of TNG's final season which portrayed the events of the average Star Trek episode as seen through the eyes of junior officers.
Originally, Reg Barclay was considered to join the team of lowly Starfleet officers serving aboard the Enterprise-D. It would certainly be interesting to see how Barclay interacted with those who weren't senior staff, but the writers wisely decided to excise him from the finished script. Ultimately, Reg Barclay was so well known by the time of TNG's final season that he would have stolen the limelight from the other characters.
Given that Lower Decks was a fresh take on the regular cast through the eyes of unseen characters, it would have lessened the appeal of the episode's unique hook if Barclay had joined them. He should definitely still show up in Lower Decks, though.