There is no OOTB functionality but you can implement your own.
You can ask user to lock page if they are working.
and check whether page is locked by same user or other user user while creating workflow by making Ajax call to your servlet which will return true or false based on state of page and display popup message.
With Touch UI - you are correct - you can run a workflow on a page - even if its a payload on another workflow. To block a workflow on a page that is already subject to a workflow - you would need to write a custom service using this API -- WorkItem ("The Adobe AEM Quickstart and Web Application.")