The dream of Mythic is basically dead... Frost Interview with Yoshida

[Rilifane]

4 man mythic style would be pretty cool. I personally am not sure I would be able to clear that content, but I think it makes sense to have multiple paths to work harder to get better stuff (e.g. raids vs crafting), so long as the gap for casuals like myself is not so huge or we will just feel bad haha

The beauty of mythic style 4man dungeons (and scaling content in general) is that it catches part of both crowds. Right now a single person can easily carry an entire run. In 80s content even both the healer and tank can be hilariously bad and a dps can carry that. Mythic style dungeons would start barely above that level and can go anywhere from there.
I don't think their "we want good players to be able to carry runs" is a good argument when scaling is up to them and higher difficulties are not designed for deadweight squads anyway. We really need more midcore content and that would've been a great opportunity to bridge the gap between casual and hardcore.