I just purchased a Roku TV and after spending sometime with it i found a few limitations that are a bit bothersome.   I'm not sure if the forum is the correct place for feature requests, but i searched and saw there had been such posts in the past.  anyway...

1.  SSA/ASS Subtitle support.  I watch a lot of anime, so this is really limiting.  I imagine it would be better for roku's ad revenue for me to stream directly on the TV instead of my xbox?
2. Disable Motion Smoothing.  it's not a problem for inputs since i can enable game mode, but for streaming it makes all the movies look like soap opera's.  It was really disappointing when i bought a $20 4K movie and it look so bad. 
3.  HDMI Black Level. The blacks are too dark on my ps4/xbox.  This looks good for movies, but for video games it's too dark.  I've tried adjusting brightness/contrast, but even with it all the way up some dark objects are too dark. Honestly I've been playing around with it for a while, and i'm pretty sure the tv auto switches depending on what the output is but no mater what i can't get it to look quite right.

2 and 3 could be implemented in the Expert Picture Settings of the app.  It's a bit weird that these aren't already options, but extensive white balance and colour space setting are...