Sankey visual should support a key field to show flow of group through whole diagram

The current Sankey diagram allows me to visualize groups of users as they move through stages in my process and understand the volume. However, since the diagram doesn't support defining a key value, it can't be used to track anybody through the entire process.

I have a dataset that contains a starting value, an action, and and ending value for each customer. I can use the Sankey to see which action a group of customers with starting or ending values took, as well as for an action, see which starting/ending values they had, but I can't see pick a starting value and see which actions they took and which ending value it flowed through to. In my case, I want to understand the customer lifecycle and without a key value, the current Sankey chart won't let me do that.

Please!