Proprietary video formats certainly aren't dead yet. MP4 is still the most common format by a long way in web work, for example.
I think it's clear which way the water is flowing, though, and I don't think any amount of distress on the part of the fading powers of yesteryear is going to change that. There is too much incentive and too much technical expertise on the other side, and that side also has enough big players with their own legal teams to block attempts at obstruction by questionable legal challenge.
But don't underestimate what a firehose of money can do, especially one in the hands of which is effectively a dying industry. (A small one, for sure, but one that was formerly extremely profitable)
The big players are can bring significant resources to bare to be sure, but they're also the least committed fundamentally. The right extremely beneficial licensing terms for say, HEVC, in exchange for dropping out of AOM would probably be extremely uhh "business smart" for more than a few of those big names.
One of the challenges in this space has always been that patent licensing for existing codec has zero marginal cost. Vendors can respond to the threat of open alternatives with licensing concessions. I think part of why we see the system collapsing a bit now for video is because they've managed to thicket themselves to the point where its become extremely politically difficult to negotiate in that manner.
I think it's clear which way the water is flowing, though, and I don't think any amount of distress on the part of the fading powers of yesteryear is going to change that. There is too much incentive and too much technical expertise on the other side, and that side also has enough big players with their own legal teams to block attempts at obstruction by questionable legal challenge.