Might be worth posting as a suggestion if it hasn't already been done. If there's anyone you trust that has an IPB or vBulletin license you could ask them to convert for you, then you could use the converted db to import to xenForo. Best of luck!
And why wouldn't you advise waiting for an official converter ?
An official convert would cause less problems than converting twice (MyBB -> vBulletin, vBulletin -> XenForo), and you would have support in case there was an issue in the conversion process, or was an issue with data after conversion; the same cannot be said for what you suggested.
A third party convert, like what is available for SMF and punBB is another solution, and will often get support from that creator, so that is another alternative. The problem with this you cannot be assured of code quality, and it can be troublesome in and of itself.
His best bet is waiting for an official converter, or waiting for a 3rd party converter, or as a last option paying for conversion.