Thanks for the feedback @simonwidjaja!
Indeed, we don’t apply some validations on draft content, “required” is one. We identified that the work on draft contents often takes several days and involve several people depending on the workflow. And as @DMehaffy mentioned, we decided to make it more flexible by removing some validations, so a user can just work on a part of a content and still be able to save.
Right now in the first version of the feature, we didn’t implement options to select whether validations should apply or not to drafts, but that’s definitely something we’ll think about for the next improvements.
Now regarding what happens when someone disable the D&P feature on an existing CT, we put a lot of thoughts into that haha 
Again, for the first version and to limit the complexity we enforced deleting all the drafts. The reason is to avoid making all the draft contents accessible through the API if someone disables D&P, which can be critical. But still let the possibility to update all the drafts and publish them to avoid losing them (which kind of make sense, if you want to keep them without D&P they should be ready to be accessible)
Here again, I’ll put your feedback in our list of suggestions to improve the feature, which could be useful to have several options 
Thanks!
And glad you like the feature