I sent a follow up to support and was told to contact Sling about adding support for my Roku. It doesn't seem like Sling is supporting any of the newer Roku devices so I wonder if they even care. When I was at my local Best Buy I also noticed they aren't carrying any Slingbox devices.
While it's not ideal, I have resorted to plugging in my iPad via an HDMI cable. Really annoying and it was just fluke that I even packed my HDMI / lightning connector for my iPad, but it's better than not having my Slingbox on the TV at all. I also can't find a way to prevent my Roku from updating, if it hadn't updated on Jan 15th I'd be fine. If they ever bring the option back to connect to my Slingbox, I'd like to be able to not update my Roku again after that but seems like there's isn't a way to turn off automatic updates.