While I didn't like what TCW ultimately did with it and thought FOTJ's "explanation" positively stupid, I actually don't mind Mortis in principle when approached in a more abstract way. If it was something mysterious encountered for the first time in a film (sadly too late for that now of course), then I think it actually could have been rather cool in a fantasy/sci-fi genre blending kind of way. I mean, the ST needs to do something other than ghosts and laser swords to make it fresh and exciting again, and Mortis could have been just the thing to make it different to every other science fiction series with lightsaber derivatives and telekinesis these days. But Lucas blew it by using it too soon in TCW, so now the ST needs to think up something different. Although I suppose they could always have the new protagonist visit the Whills or something for a similar "spirit realm" kind of thing.