Not quite sure what you are trying to say.
Are you intimating that it is not worth any writer to take an established series and try to expand it?
Perhaps actually move on in regards to characterization that hasn't changed in X amount of years?
Both series needs this immensely. Especially Outlanders.
Reading David Golemon's EVENT series, which reminds me strongly of the Cerberus crew, is kinda a perfect example. In the EVENT series, there are two main characters, much like Kane and Brigid, who actually move their relationship along throughout the series. With only a recently new 8th published book, Colonel Jack Collins and Archeologist Sarah McIntire of a secret group fall in love, have issues, and have gotten back together again - in just 8 books! Along with all the sci-fi action/adventure that makes this Best-Selling series a page turner.
I don't see why in this series the two main characters, Kane and Brigid, can't be sexual beings AT ALL. If the powers at large are afraid to have the writers write themselves into a box, then just have them have casual sex on the side. Or just act human - by having, at the very least, sexual thoughts and feelings towards something or someone! Everybody else - including nerdy Lakesh - is getting laid.
But not Brigid and Kane.