Ability to reference indicators in other chart panels

At the moment if I have a custom indicator in the upper/price panel and I want to use values from another indicator in a lower panel, the only way I can see to do this currently is to create another instance of the lower panel indicator in the code for the upper indicator. This seems wasteful and could affect performance if the same calculations need to be performed multiple times for the same bar.

Instead it would be great if we could give each indicator instance an id or tag, and then use that tag in our indicator code to fetch a reference to that indicator instance so that one indicator (in any panel) can read the DataSeries values from another indicator (in any panel), without duplicating all the calculation work again.