Wow, this is fascinating, dxb!   Er, don't estuaries contain effluent, or used to? (I was wondering if that had something to do with the appellation!) I saw one thing that would definitely set my teeth on edge: the change of /st/ and /str/ to the sound of /ʃ/ in she. SSHtation? SSHudder!
The disagreements sound like the everlasting ones between the old-fogey-sticklers and the young up-and-comers who say so-what-if-it-ain't-like-it's-always-been-we-like-it-this-way.
I thought it was particularly interesting that some young people like it because it "blurs social lines".