IMO, all of the cable channels that are bundled with packages from providers like Comcast/Time Warner, etc should get on the Roku band wagon and offer up a la carte pricing for their channels through Roku. This would be the way to 'cut the cord'. Choose the channels you WANT to watch not what your 'given' to watch. Add them to your Roku and away we go. No more, 'get 200+ channels' when you only really watch 5. Hopefully this will come to fruition in the near future.
But those chs are guaranteed income from the providers where income from a Roku ch would be problematic at best. Also there are contracts that probably prevent branching out like you suggest.
In the mainstream media risk taking is a nearly lost art and it would take vision for existing cable chs to branch out.
However, as the contracts expire, we will see more of those chs created as the providers can negotiate deals that include do not include streaming exclusions. The risk for that is much smaller that trying to go it alone on streaming.
As far as live streaming it really only applies to news and sports because almost everything else is recorded anyway. The Roku is gaining those but it will be a gradual gain. Fortunately several of the mainstream and high dollar sports have already shown up and we can hope for more.
The really big step would be for foreign sports that are high dollar to show up. European Soccer, Rugby, and even Japanese Sumo would be a great addition.
It will be a gradual process but the MLB, NHL,MLS, NBA, and other sports chs are a good step and the news chs, although much slower to show up, show that streaming is moving forward in the "live" department.