So you can pretty much use the browser to replace the output and include some neat features, given that you have to understand some javascript to do so. Does anyone know the more technical pros and cons of using the browser compared to using the output panel? Overall so far all I can see is that output panels have the ability to log natively.
Some system messages, such as the "You've taken a screenshot" message, go to the output and cannot reasonably be redirected to a browser control.
Yeah, there's a lot of things that go into the default output that can't be redirected, but outside of that... there's no real reason I can think of.

There's a few limitations you need to be aware of, such as IE's URL length limit which is 2,083 characters. So even though GET can handle up to 65,535 characters, your links above 2,083 will be truncated. You'll need to split messages up taking this into account.

You'll need to use browse_rsc() on images you want to show, including those using \icon. You'll also need to handle links in a special way, as just clicking an href link would open it in an IE popup, or the output window itself. So you'll want to catch links and send them through BYOND's link() to open them in an external browser.

Stuff like that.