I haven't read through the whole thread at this time (simply because there's too much to read), but I only was made aware of XenForo due to the announcement made on vbulletin.org. And while I'd love to be able to purchase a copy upon release, I amn't able to afford to do so as of yet. I was somewhat neutral towards IB (although had questioned a few of their practices), but given I'm now made aware of what they're doing, I'm not terribly impressed with them, and I'll be switching to XF as soon as I possibly can, although ideally, I'd require some sort of CMS solution before I can properly begin to commit to a switch. I am looking forward to learning about the API in the meantime and learning how to make my own add-ons as well! It certainly seems easier to code for XF compared to vB, from what I've read.
I am impressed with what I see so far, and think that XF deserves to be successful, as the devs and other staff genuinely care about what they're doing, and this is something I can get behind. It's a shame what happened with vB though.