For the most part I understand how this talent works decently well. For lower gear levels, it wasn't optimal for elemental so I didn't look too much into it and now that I'm getting into 495+ ilvl I'm thinking it's time to start looking at it. Is it totally independent of mastery, or does one of these entities affect the other? Meaning, does mastery lock you out of an echo proc and vice versa, or is it possible to eventually see a stream of constant lava bursts at highest gear levels?
You can't get infinite procs; Mastery procs "first", then Echo, so Overloads can Echo, but Echos can't Overload. On a single actual cast, you can get up to 4 "casts", with EotE; the original cast, the Echo off of it, the Overload, and the Echo of the Overload. In the end it's basically close to neutral with regards to stat weights; it isn't going to significantly increase or decrease the benefit of Mastery relative to other talent choices in that tier. You'd probably see some slight variations, but not the big jump you would if it were possible to get infinite chains or if Overloads just couldn't proc Echos.