The Champion didn't not have to show up every show, and besides Taker made every show when he was the champ in 2002, and guys today show up often on both shows as it is.
The main event roster is much deeper with one title, you get far more combination of matches, two titles worked well when they had a far deeper roster. But they don't these days, so they have to recycle the same match ups over and over again.
Or they could come up with long story lines like they did in the 70's some of the feuds lasted a year or longer. The problem is wear and tear on the bodies. It was fine when they have 30 people not 60-80 like they do now. They will certainly cut the roster down to 30-40 people or less to do this.
I see the point of more depth but the order of depth starts at Cena, Orton, Edge, HHH, UT, and so on. So we relive the 80's with one champion for multiple years. It will be applauded but as soon as Cena gets the belt for 6 months every single one of you will be asking when will they split the belts back up and what happened to the Miz's push or JoMo's push or where did Koffi go. Alot of the younger guys will disappear or will get put in the back burner and so much for the youth movement, it dies with this single action.
With two separate titles you get more people involved and more pushes to see who can hang and who cant. It is still somewhat separate. If having the champion on both shows is so great with all the travel and extra work for the people on the shows going back and forth. This might just be the reason besides the movie money that the Rock decided to walk away. He and SCSA where doing both shows at the start, they could have got burned out, and injured which they both suffered alot of and it shortened their careers. Vince was in the i have got to beat WCW mode at all costs and shortened the careers of two of his biggest stars ever.