Main Extra sounds like what used to be (FULL) Y, with higher upgrade priority, fully refundable tickets, earlier boarding, etc. Way back, some airlines distinguished "full fare coach" and gave it special privileges before it evolved into business class.

I'm anxious to see an enumeration explaining how these new "experiences" are modified for elites of different levels. For example, will elite status boarding zone pre-empt the boarding zone attached with these new experience types of fares/

Basic, which I assume is just what we now call BE, always had (negative) features that overrode normal status benefits. With the new terminology, Basic seems closer to Main.

I guess the good news for now is that "Basic" is only associated with Main Cabin and not (yet?) PS/D1.