Yeah I tried to look around and found more people talking about DS-Lite, seems to be easier.
MAP-E config is not really a secret, because when I log in the rental router some important parameters are already there, and then the rules are pretty much based on standard IETF calculations, i.e. everyone would be able to calculate.
However all those Japanese websites I found, they started to test MAP-E on 19.07 or even earlier but I couldn't get success by following instructions, while most of their "successful screenshots" are gone (maybe too old, server removed), it was a pain for me to setup the whole thing.
In some not so busy areas, like me living in Kanagawa, it's also not too much difference. While I heard from some people living in central Tokyo, especially the "closed down" dates during COVID, working from home with or without using IPoE can show significant difference. I didn't feel that it was probably far away from Tokyo, however I noticed that PPPoE is using single core so even my Celeron N2930 based x86 cannot achieve > 750M, but with IPoE, the thread limiting factor is gone, I tried to use my Linksys WRT3200ACM (7 years old!) and I can get ~900M easily.