Ultimately it really is about usability and while we might have gotten comfortable with old designs, they didn't necessarily work for newbies. Certain peeps mentioned the possibility in recent posts and the thread kinda drives the point home IMO. It's not really about you and me - we overcame the inherent issues that the majority of peeps in the studies pretty much give up on.
I really don't think there's any going back to the old design for LJ. Towards the end they also clarify the difference with offering site schemes vs. multiple profile designs and on the technical side, each is a completely different issue.
LJ can't offer opt outs for everything - in the long term it means increasing fragmentation and development time and probably also changes in the future that might be incompatible with older designs >_>
At least they're willing to take feedback for improvement, which is something rarely seen with other sites.