They are doing no such thing. [...] PPAPI (Chrome / Opera), NPAPI (Firefox due to be phased out), and ActiveX (IE due to be phased out).
Did you just rebut my claim that plugin support is being phased out by mentioning three incompatible plugin systems, two of which are end-of-life? Neither Firefox, Microsoft Edge (nor Safari for that matter) are slated to gain PPAPI support.
PPAPI plugins are only supported in Chrome and its variants, and usage is dismal. Of plugins that were most popular just two years ago, neither Silverlight (end-of-life), Unity Webplayer (end-of-life), the Google Earth plugin, Java, the Google Hangouts plugin nor the Facebook Videos plugin are available as PPAPI.
PPAPI is in practice an internal Chrome API to be used with built-in modules (not plugins) such as Flash, the PDF viewer and NaCL.