iBr

Another nice feature would be changing the member's primary group but kicking their previous primary to a secondary group.

I just think you would gain many customers if you filled the gaps. If IPB had everything vB had plus more, customers would have no reason to use vB instead. When I told my friends that I purchased an IPB license they were all disappointed because they claim vBulletin is much simpler and has some good features that IPB doesn't have, plus a lot of add-ons. Also, to your question, yes. 'Infractions' are a big part of vBulletin and many big communities use vB instead of IPB because of them. When I bought IPB I thought the warning system was improved, but it's practically the same as it was before.

Actually, the single most important feature that converting users would probably want is the layout.
A lot of people like the horizontal poster information better than the vertical.