(((interference)))
Veteran
The problem with such expansions is they don't get properly used. Devs have to design for the minimum spec, and then spend extra to support a higher spec console. I suppose for texture fidelity a RAM pack is an easy-to-accommodate upgrade, but that's the only expansion you could comfortably fit, and you be better off putting such an expansion on a proper internal bus designed for the purpose. No need for cross-device portable connectivity such as Lightpeak for that! We haven't had a RAM expansion or anything close for 2 generations, and I doubt we'll see a return. The closest we got was Kutaragi's hopes of networked boxes over Gigabit, that went nowhere.
Well, they got properly used on N64 and SNES (Perfect Dark, Star Fox) - of course not everyone is going to take advantage of them and will just tack on some enhancements or ignore it completely but there will always be the technically inclined studios who want to squeeze every last drop from the system and they will see it being put to good use.
I agree that any add on would have to slot into the motherboard much like the cartridge slots on old systems.
But your right we're probably not going to see anything like this next gen.