I expect JPEG and PNG to become for images what MP3 is today. And I expect H.264 to become that for video. These formats are too ingrained, whatever their technical limitations.
Technologists consistently underestimate the power of backwards compatibility. Itanium was better than AMD64, DVORAK is better than QWERTY, and I'm sure Esperanto is lightyears ahead of the monstrosity that is English. But backwards compatibility always wins, because it fits what the world was already designed around.
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(To be fair to GP, they said Opus is the definitive choice for the web, which may be true for integrated in-browser playback. But in other contexts, well, Amazon sells MP3s, not Opus files.)