This is what I was trying to get at. There is a difference between features that are aligned with Bitcoin's vision and features that actively work against that vision.This is a bit of a special case because the importance of 0-conf transactions is explicitly stated in our Articles. So on that basis we could have an exception to our usual behavior of configurability. But I'll go with whatever the community decides here -- its just as easy to add a configurable as it is to comment out the code.
If core included a new feature that enabled double spending previously confirmed transactions for a higher fee, should BU offer that as a user configurable option? I think most would agree not.
Somewhere there is a line between features that are OK to add as user configurable options and features that are not OK. There are some things (such as the above example) that just are incompatible with what Bitcoin is.
I don't know where that line should be, but it does exist. RBF is close (and I'd say over it IMHO).
I think there needs to be a very simple and clear vision statement on where BU wants to take bitcoin. From there decisions on which features to enable or make a user configurable option should take into consideration that vision statement, and features that actively go against that vision statement should be rejected. For me the vision statement is to fulfill Satoshi's original vision of a global P2P cash system that enables instant transactions between users and is directly usable by as many participants as possible.