And if a plugin is needed, well it defeats your objective.
As for whether it would be good to do if you could - well it’s also not very aligned with the objectives of the project. It would be OK as a side-effect, but it’s not a core objective I think (to support existing internet infrastructure).
Nope, SAFE network is made to be distributed and anonymous. There is no in-browser technology that can support this natively. WebRTC is neither distributed (by itself) or anonymous. Also, the browser is a bad development platform for those wanting the security features of SAFE due to the extreme attack surface. There are efforts to make alternative browsers were you still get the benefits of the web platform + SAFE without some of the security concerns of the traditional browser.