As a developer I understand that each supported filesystem adds development workload and potential for bugs and at some point you need to weigh this cost against the benefit. The problem with this is that the people who use these filesystem are more likely to be opinion makers for other people in the choice of file syncing solution. Dropbox is big enough so they think they do not have to worry about it. But there is a real possibility that they will alienate just enough influential people, that this will erode their user base more than they realize.