i haven't opted in yet, too worried they are gonna wipe everything as a necessity and i prob won't actually play a game till it's live, glad to see it is working well so maybe they won't have to wipe it.
If I recall correctly even if they wipe you should still be able to keep the races you have already downloaded.
Still may not be compatible. They may end up needing to throw extra data structure in the files.
I'd imagine the files will be easily reworked by the author to make them compatible, and just another quick download away. Support wise, I'm glad they are warning everyone this is a possibility. Although even with this warning, if they do end up needing to wipe, I predict there will be a large number of complaints and WTFs inbound.