I don't know if a shill-free alternative to Reddit could ever exist- I tend to think the openness and scale of Reddit (which is the whole point of it) is what allows shilling to occur. It really bums me out.
Sure, but I think that is actually a very difficult problem: how do we determine whether a comment is being sincere or not? Furthermore, assuming we had a foolproof method to do this, would the site have enough funds to use it routinely and ethically? I think this is the problem we're seeing now with a large number of tech companies.