Very true on the business process user initated workflow feature.. I do miss this in cloud.

However, a workaround for this would be to have the users trigger workflows by adding a tag to the documents.

Not as easy as a BP but achieves the same result, well kinda...minus the reporting.. but users can initated WF's.

Once the desired workflows starting events have been configured to start on a specfic tag set the user can add tags via the details tab on documents / folders.

Just make sure to remove the tag in workflow once initated. 

Good Luck!