It would be great to be able to configure tenant-wide variables (maybe as a tab in the settings section of the tenant). This would allow creating variables accessible in all forms/workflows that define legal disclaimers or even image urls, so that when updated in this one location chages would be automatically be reflected in all forms.
(Not sure how feesible this is as unsure if the workflows/forms would need to be republished to reflect the variable change).
Gavin Adams commented
very similar to the nintex sharepoint on-premise workflow constants and is really needed.