Works!
On my Mac, the folder is in ~/Library/Group Containers/UBF8T346G9.Office/Microsoft/AppData/Microsoft/Office/15.0/OfficeFileCache .
I deleted that, rebooted, and OneDrive for Business launches normally.
This did indeed happen after installing Office 2016 Preview. I've submitted feedback via Word's feedback feature — I suggest anyone encountering this do the same so to give the developers a chance to squash this bug.