Good roundup, thanks Reg! I recently had to do an editing piece, thankfully only at 1080 not 4K, and did it in Blender on Ubuntu. Really powerful, if a little flaky.
As you've pointed out though, the hardware demands are high! Which puzzles me, thinking about it. I first did digital video editing at school using Avid on a PowerMac with two huge 20" CRT monitors - it seemed revolutionary at the time, but it was speedy and responsive, more so than my i7 with 12GB of RAM and running from SSD. I realise that those years ago it would have only been low resolution PAL video, but still why does modern hardware feel less capable?