Without having to watch the video, will USB 4 be backward compatible to at least 2?
Take a look at the connector in post #2. I'd have to say "no". You'll need new hardware. Until someone creates an interface that will have ports to handle the connectors and facilitate the new speeds. If that's even possible.
I kinda doubt it................The cable mfrs gotta eat...............
When 3 came out, there were those non-end-for-endable cables that shipped with, for example, the Seagate drives (the external Seagates that had those changeable bases, so the user could use the base drive with various different interfaces). That worried me. That got changed. Not a bad idea to buy a couple of those cables (one connector looks normal, the other has a sort of dent in it) and toss ' 'em in the just in case pile. Anyway, yes, USB 1 through USB 3 will work on a USB 4 port. If we see any machines by Christmas which have USB 4, they'll probably be spec-bumped expensive game boxes. There won't be any speed difference between the usual speed of the USB 1 or 2 (or 3) peripheral and plugging it into a USB 4 port. I'd be surprised if the USB 4 hubs don't take advanage of the greater bandwidth, and offer a ton of ports but broken down by 2, 3, and C.