I've personally seen enough of Orton as a "heel" champ, and want to give him at least a nice run with the belt before I can pass judgment one way or another on him as a true face champion. That being said, I think things have worked thus far with his current character.
WWE hasn't truly pushed Orton as being a "full out face". He's lost none of the characteristics he used as a heel, other then having his lackeys around. He boasted a few weeks ago about "not being an honorable man" and the people he's punted. "Some were deserved, some were not.", he said without remorse, and proceded to punt a helpless Chris Jericho a week later. Not exactly the characteristics of a face, are they?
What changed for Orton, and WWE, was the CROWD RESPONSE. More people began cheering Orton rather then booing him, forcing their hand quite a bit. Do you ignore the obvious crowd response, or do you give the fans what they want? I think WWE has done the latter, without changing whats made Orton truly successful.
I think what WWE has done with Orton has been excellent booking. He's being booked as a "one man army" type of character, which is a departure from him in the past. In that essence, he is a face, as he's not relying onm others to do his dirty look. But hes being booked as cold, remorseless, and as caring about noone but himself, which are certainly traits a heel brings. WWE(and Orton) have done a nice job of combining the 2, which have made for a compelling tweener character.
I think its working, and evidenced on the crowd reactions, Im not the only one. So why mess with what's already working? Every wrestler, in my opinion, deserves a full run as a face and a heel in order to see what they can do with their characters. As far as Orton's heel character, what more could they have done without him growing incredibly stale? He's in a perfect place right now.