Is it possible to keep critical data on the original filesystem ? Why not exclude some folders from /data/data ? I know it will complicate things, but why not look into it? I don't need my contacts, calendar, email databases to be that blazingly fast... I find it more important that they are save. So why not giving the possibility to exclude these from the trick?
Most people do actually want their contacts, calendar and email to be blazing fast! Me especially.
There are still no known issues of data loss - but if it is a problem for you, consider syncing them with google, or some other provider. I don't really know what would happen if you lost only part of /data/data, I doubt it would be any different from losing all of it. So it doesn't change much.