Would it be possible to tweak the forums to dynamically widen the body of the post on wider screens? As viewed on most monitors, it would be nice to see less horizontal scrolling/fewer line wraps in posted code instead of so much white space on the side of the page.
Not at present. Keep in mind that “most” monitors are mobile devices these days, not that monster 42" on your desk. 
The site theme is responsive to a point, but in a mega-wide window, it does limit itself. It’s a bit more complex than just saying “go for broke and be as wide as you want;” it takes a lot of planning and coding to make the site work at iPhone width as well as “infinite,” and we just haven’t gotten there yet. If you’re good at CSS and WordPress theming, we’d welcome your assistance.
That said, there’s also some limitations on the code display that are separate, which is why there’s a button at the top of code listings (if the author has bothered to use the code formatting) to pop it up in a plain-text window.