[azakai]

That's a different form of diversity, but yes, plugins do give more options. And they are helped by running in browsers.

But they are security risks and cause lots of problems for browsers, as well as the monoculture issue (I can't run Flash on linux anymore because they decided to deprecate the flash linux NPAPI plugin).

So I don't think browsers should promote them. But native apps are still fine for them - Unity is flourishing especially on mobile, far more than on desktop browsers; Unity ships native apps on mobile.