Personally I hate the idea of a movie and really hope its not turned into one. Now before you string me up for saying that, here is why I say that.
1- It would have to be severly censored for a mass theatrical release which would in turn ruin the film since the adult content is what is part of what makes it so charming. Censoring it would ruin the story and characters. The violence and depravity is as much a part of the story as the people are. This is one of the very rare times I would say violence and sex actually help the story. Yeah sure it could be uncensored on dvd or whatever but thats not the point, besides if they didnt add any new material in all the uncensored stuff would equal about 50 minutes worth of showable material.
2- It would have to be like 4 hours long to fit all the material in. Cutting out stuff would hurt the story and characters since all the misfortunes and good things that happen are what make the characters more likeable or detestable, even the little guy who screws dead meat is important to the story. The whole thing with its small nuances read over the series is what helps draw you in and appreciate everything that much more.
3- I dont think it would do well financially enough for anyone to invest what needs to be invested in it to do the project properly or even make it 2 films. Sure us hardcore fans really want to see it but most people dont. The general public wouldnt get it, all they would see is the cursing, the violence and so on, the whole point of the story and the relationship you build with the characters would be lost on them. People (at large) want something thats easily digestible in 90 minute segments.
4- The whole theme of god turning his back on man and the quest jessie takes to kill god will piss off more people than you imagine. Especially if they kept in the original ending [SPOILER!!!!!] then the saint of killers, a man who was used by god and cast aside will kill him. I dont think that will sit well with the christians at all. All the relgious zealots out there will be running around in a tizzy because of this. People will not be able to handle the god hating and god condemning overtones, I know some will say sure they can, but they wont. People as individuals are smart but in groups they are insane and stupid, especially large religious groups. They have no sense of reasoning as a whole (sorry wasnt making fun of anyone who is religious, just illustrating a point).
5- The story, content and such will be altered for a movie. You can not (to me atleast) make preacher any better, you can only make it worse by tinkering with it. Time constraints, ratings constratins, studio execs, movies run time, producers, writers, director and all these other facts will change the movie and personally you cant change it for the better.
At any rate, I would rather see this not get made now because its potential for failure is huge. Id rather not see it, than see it made and just crash and burn and thereby ruining any other chances of it being done right. Its just a big and complex thing thats to much to digest in movie format really. The HBO series is still the only viable option in my mind, it was perfect. The total freedom of being on HBO, the episodic content where everything has room to be in it and not hampered by trying to censor it down to a R rating for theaters.