I hope it will handle any and all obscure camera formats natively. Don't forget TOD as well. There's all those strange things consumer cameras record in their .avi wrappers as well. I'm sure we'll get postings about what is/isn't handled as people bump into them.
There there's those other weird formats that businesses hand you because they have no masters. Those might include Real Media, Windows Screen and Windows Image formats. Windows Media using GoToMeeting codec. Alas I don't expect FCPX to handle them because of the lack of availability of decoders that can be integrated with anything.