Ok, this is beyond the scope of what most live stream producers would ever need in their workflow, but the Evertz Dreamcatcher is pretty damn cool.
The Dreamcatcher is a 48-channel 4k instant replay system that you might find in use at say, the Super Bowl. As you can see in this video, an editor can easily scrub to a point in live captured footage and then select a portion of the frame as your edited output. If you’re shooting with 4k cameras, you can output that selection as full resolution 1080 HD. Not a bad trick, if you can afford it. No idea how much these go for, but you can bet a fully kitted system is in the 6 to 7 figures.