Tom Welling would bring 10 years of bad writing baggage with him. And isn't Welling a producer on Smallville? It'd be a slap in the face to him to bring him onboard a movie and tell him they want to ignore Smallvile.
Not necessarily. Producers aren't always strictly loyal to a single interpretation of a fictional character. Most of the major talents who created the DC Animated Universe have gone on to create or produce DC-based shows in incompatible continuities -- Bruce Timm on the DVD movies, Alan Burnett and Stan Berkowitz on
The Batman, Glen Murakami on
Teen Titans, James Tucker on
Legion of Super Heroes and
Batman: The Brave and the Bold, Paul Dini on
Krypto the Superdog, etc. I think the people who produce shows based on comic books are fully aware that they don't own the characters, that they're just taking something that's been around for decades and offering one variant interpretation of it.
Meanwhile... I just watched the extended cut of
Superman: The Movie, wanting to reassess it (and to refresh my memory since the Donner cut of
Superman II is coming up in my Netflix queue), and it made me wonder more than ever why anyone would think Brandon Routh was a worthy successor to Christopher Reeve, let alone in a film that was supposed to be a rough continuation of the same continuity. Reeve did a masterful job playing a Clark/Superman who was corny in a very Silver Age way yet completely sincere and charming about it. He had this utterly self-assured amusement, this enjoyment of the little joke he was having with his dual identity, that was nonetheless totally good-natured and innocent, not condescending or mocking in any way. It was a splendid interpretation of Superman, and of course he did a fine job differentiating Clark and Superman. Next to that, Routh was just... one-note. He didn't convey that same spirit or charm or humor at all. He didn't inhabit the role as effortlessly and comfortably as Reeve.
Of the candidates on the list (the ones I'm familiar with), Bomer's the only one that I think could come close to that same kind of charm. Maybe Barrowman could capture the wit, but he tends to come off as a bit full of himself, something Superman would never be.