I've been touting Manganiello for Superman (if they go with a new actor) but now that Brandon has filled out more and looks more mature, I'd be more than happy if they kept him for the role also. I personally thought he did a great job and did the best he could with the script and story he was given. It was his first major acting role too, he has a bit more experience now.
As far as confusing the audience by putting the same actor in a new type of Superman film goes ................................. that excuse is lame and tired. People should be given more credit than being idiots.
The first 4 Batman films (from Burton, Schumacher etc) had 3 different actors play Batman - Michael Keaton, Val Kilmer and George Clooney. Viewers were able to get their head round that.
The James Bond films had numerous different actors but at one stage they had two 007 films (one with an older Sean Connery returning to the role, the other with Roger Moore continuing) on release at around the same time. Viewers were able to get their head round that.
That's just two examples - I'm just trying to make the point that the vast majority of movie-goers will not be that confused by keeping Brandon in the role whilst simultaneously trying a new approach to the Superman movies.
You can't read a single interview or article about Brandon Routh without hearing Superman mentioned somewhere. It's an iconic role and for the vast majority of Joe Public - who don't frequent forums like this and don't have any idea of the extensive list of potential Superman candidates us fans are throwing in the mix - Brandon Routh is Superman. It will actually be less confusing for them if he is kept in the role.