The first would be the ability to shuffle a playlist. I loved that shuffle was added episodes a while back.
This is possible today with the current release.
Click on your Playlist library. Then, on the grid of Playlists, highlight the one you want and instead of pressing "OK" press "Play" on your remote. It'll shuffle play the highlighted playlist.
For the subtitle one, I'm unsure what capabilities the API offers us and what functionality Roku would support, but it's at least worth taking a look and seeing what's possible.