I've not played using LRB5 (still not any good at LRB4 yet, so not bothered about 5), but it seems to me that opinion is pretty much divided down the middle about it.

Personally I don't see what the problem with FUMBBL switching over to LRB5 is, assuming it ever happens.

Surely there will be more than enough people who still want to play LRB4 that there will just be a "classic" division, which still plays by the LRB4 ruleset.