Being a Lead in an hour-long television show is a full time job. And not like "parenting is a full time job" which it is, but an actual bonafide, you have to be there and give it your all 40+ hours a week or don't come at all.
The closest example I can think of is when Smallville and The Fog were being filmed at the same time. Tom Welling ("Clark") had a month where he got between 2 and 5 hours of sleep on any given evening. The entire rest of his existence was filled with traveling and filming (food in the car or eating would cut into his 2 hrs of sleep). This was only possible because the two production companies wanted to work together AND the Fog tended to film night scenes while Smallville tended to film daytime scenes.
So as such, I'd have to say it is definitely NOT possible for one person to headline two different hour long dramas at once. Scheduling conflicts (one show can't shoot the love scene because the actor's shooting an action scene right now), actor fatigue (we're talking about 80 work weeks at this point) make it virtually impossible. Now, when you talk about things that are less demanding, like being a recurring character in another show, or doing a cartoon, or a half hour sitcom, then you start to get closer to the realm of possibility - ONLY if the two production companies work together seamlessly.
Now, if a single production company is shooting two different shows, then perhaps you have something. Probably not, but perhaps.
Short version: The main problem is scheduling. Any two-show deal will break down as soon as both of the shows have a 3:00PM scene to shoot.