Can you tell me a little more about this? When would you use this? Do you mean that you could take one of the formula expression rows from one Formula tool and add it to a new expression row in another Formula tool?
Yes, the idea would be to drag a formula row from one tool into another tool and have it appear as a configured formula expression in the second tool. This would be useful if you have to have the same formula in several places in a workflow. One use case would be if you needed to add a status field to parallel streams of data. The case that prompted the idea for me was moving several formulas in different parallel processes to one formula tool later in the workflow after the data paths had been joined together.
Thanks @Vadim, I hadn't ever used the recent expressions, and it takes me close enough to what I need that a drag and drop solution would be redundant.