1. It has to be affordable to attract as many customers and converts from vB and IPB as possible. I would suggest to price it below $130 as a grand opening deal just to beef up customer base.
2. Team XenForo needs to have several languages packs ready before its first release. I would suggest Spanish, German, French, Arabic and Chinese. This can be done in less than a week if professional interpreters are hired.
3. XenForo needs to foster a modding community.
These are just few things that came to my mind.