I was one of the early mods on programmers.stackexchange.com that was kinda-sorta aimed at being just that. Some participants wanted explicitly that, where offending questions would be automatically moved to P.SE. Others wanted "anything that'd be off-topic on SO" as the key criteria for P.SE. A lot of the early questions there were pulled directly from previously-closed questions on StackOverflow. Over time, though, P.SE drifted away from that model due largely to pressure from the SO/SE leadership. It was made clear that free-form discussion was not what the StackExchange platform was for- it was for answerable questions.
And I can understand that. There exist a lot of places on the web to discuss technology (e.g., the one we’re commenting on now). Forums, IRC, blogs, and social media site have been around for a long time. They all sucked as a place to get answers. SO/SE built a better solution, and part of that was a strong anti-discussion bias. It worked, and there is now a great place on the internet to get answers instead of the endless morass of vBulletin sites. I can understand them not wanting to mess with a successful formula.
Oh boy, P.SE had some seriously bad birthing pains. Speaking as a former diamond mod on Stack Overflow, I got spanked a few times by a particular former and overbearing P.SE mod for migrating what seemed like perfectly on-topic questions that were clearly not great for SO.
Eventually I gave up and to this day yet I am still unclear what is considered on/off-topic on P.SE.
