Hello,
I have a requirement where the Knowledge article created user should not be able to 'publish' the article, so I have created a validation rule: 
ISCHANGED(PublishStatus) &&  ($User.Id  =  CreatedById)
I am not worried about the createdByID for now, but ISCHANGED(PublishStatus) doesnt work in validation rule. Even if I just give ISCHANGED(PublishStatus) in validation rule, Salesforce allows me to publish the article. Clearly the PublishStatus value is changed from 'Draft' to 'Online' , but validation rule doesnt fire. I did try process builder as well, but with no luck.As there are no triggers for Knowledge articles at the moment, validation rule / process builder seem to be the only way 

Please could you help me if you have come across this situation ? 

Thank you.
Rahul