I endorse all these ideas, but this is a hard problem that SO has different tacks on for years, but still faces nonstop. Given this is RStudio, an approach that may be possible here would be to make code chunks run (with suitable restrictions for security and resources) when rendering Markdown. That way users could not just copy and paste errors, but actually show them, and it would be much easier to automatically flag non-reproducible examples and add an extra dialogue before they could be posted.
Making this happen is clearly difficult—but possible—and if anybody can make it work well, it's RStudio. And obviously it'd be incredibly awesome.