So, the good news is that the videos play fine on the Roku. The bad news is the URLs to those videos are provided by a secured API. So, unless PBS makes that API public, someone takes the (significant amount of) time to index the content manually, or someone partners up with PBS, it's unlikely there will be a channel anytime soon.
My Channels: http://roku.permanence.com - Twitter: @TheEndlessDev
Instant Watch Browser (NetflixIWB), Aquarium Screensaver (AQUARIUM), Clever Clocks Screensaver (CLEVERCLOCKS), iTunes Podcasts (ITPC), My Channels (MYCHANNELS)