I have 5 256g USB 3 Flash Drives with my movies. I can only have one connected at a time to the USB port on my fiber supplied - Ethernet connected Ultra - so I am playing with various hubs - they all have compatibility issues - I wish there was a version of the Ultra that would allow lots of USB memory to be connected directly - or a powered compatible powered high quality hub so I could have it all connected and have room for expansion! Roku Rocks!
I'm not a Roku Developer but Im pretty sure there are software
limitations to mounting that much extra space. You could make it a feature request....
What I do is run a HDMI cable from one of my computers directly to my TV. That
way I can mirror Terrabytes of movies,video and what not.
This way I dont run into comparability problems either.
There might be better Hardware solutions Im just not familiar because what
I have works for me.