I'd be fine with a SMALL fee if, as others have said:
1.) They include voice chat
2.) They get rid of friend codes and use regular nicknames
3.) They provide reliable, fast servers
4.) There's a decent game selection
Also, if I'm not mistaken, one of the FPSes out for Wii right now actually DOES use nicknames for online play. Maybe Medal of Honor?
I actually think having a different nickname for each game might be better than XBox Live's system of having a system-wide nickname. That way you can kind of keep your gaming experiences separate.