Some BU proponents don't understand BU and have a lot of odd ideas about it. The main feature is that it lets the user select what the biggest block they will accept and the biggest block they will mine, instead of these being fixed at 1MB (or whatever). In practice, right now, any miner would be foolish to mine with settings besides 1MB.

The idea is simply that users can basically choose their BIP rather than having it bundled in with Core/XT. Perhaps that makes more sense? Of course users would converge on a BIP (something BIP-like proposed by someone else) - just like they converge on Core or XT based on what they see others are doing.