I associate PPPoE with dial up modems. What is the use case of this today? Also, PPPoE has been around for a quarter century: why hasn't FreeBSD delivered on it? And how is a single thread not enough to fill a broadband pipe?
So many questions.
So DSL and maybe Fiber services. Ok, but ISPs provide or endorse some device to deal with the wire. At that point you're free to firewall your ordinary ethernet traffic with whatever you wish, no PPPoE involved, no?
Despite another comment claiming this was "common" in the US, I've been on a number of ISPs in the US and never seen PPPoE used at all. Had no idea this was still going on. On fiber even!
Seems like I'd get some kind of efficient PPPoE box and put that between the ISP and whatever software router/firewall (PfSense, et al.) or "non specialized" hardware router. I suppose fragmentation could be avoided by limiting packet size a little to make room for the 8 byte PPPoE bits.
No matter what switches I toggled or incantations I recited I would not get full line speed.