I did have a go on BBs rims it's for sure very difficult and time consuming but if you do it properly it works and just about the limit. so I can confirm it's possible but I don't think many people can do it easily
I totally agree with you I suffer from the same problem whenever the server is crowded (30 players plus) I start get pit exit lag and sometimes it freezes for few seconds specially when someone is using those drift spec cars (s13, s14, s15), and now since I discovered that high poly rims have something to do with pit exit lag as scawen says I'll have to fix my mods too.
after all I don't think this decision is bad at all since we have rim editor that allows pretty good and detailed rim lip, on rim spoke we just need to get creative.