Just because you never used a feature such as virtual copies isn't much of an argument. Do you never use LR's History steps? Not in xmp. Flags? Not in xmp. Collections, stacking, etc. You know what I'm going to say.... they're not in xmp either.
So, should C1 really implement sidecars as a similar placebo backup or go the full way and store all its equivalent features in xmp too, just in case you lose the hours you've put into variants, for example? So you're committing more development time to go into features for restoring that information? And what if you mistakenly restore from xmp? Or do humans NEVER fail? Well, LR has the history steps and you can step back to before the restore. Is C1 going to need a similar feature to be written? How many real features are we sacrificing now?
As with iView MediaPro, Aperture, Lightroom and other database-driven systems, the real backup is the backup of the catalog. If your machine is unstable, your safety net is making catalogue backups more often and sorting out the underlying problem.