While only >10%-share browsers can be worth commercially developing for
In other words, ideally, there would be a "polyculture" in innovation and experimentation,
that would constantly funnel into a "monoculture" in actual final standards.
E.g. replacing JS with some other language would be such a new alternative. Open-Source-Lua-Presto, imagine that! ;)
You seriously underestimate the development time it takes to pull off such a thing.
But if you open your mind a little, you'll also see that the two opinions can also be totally compatible, just dependent on the context. For example, expanding "HTML9" (ha!) can be great for exploring, prototyping, experimenting, where a monoculture is bad and harms innovation. While only >10%-share browsers can be worth commercially developing for, because of resource constraints.
In other words, ideally, there would be a "polyculture" in innovation and experimentation, that would constantly funnel into a "monoculture" in actual final standards. Of course, that's hard to establish and maintain in practice, but you can see how they're just different perspectives.