Calculated dashboard tile: perform calculations using multiple dashboard tiles

A common request that comes up is "can we see the total of these 3 dashboard tiles?". 

In this scenario, tiles have been pinned from multiple reports, each with different data sources but with a similar use case.

They are all pinned to a single dashboard, and the users want to see the total of the values coming from each of the different systems in a single tile, so they can compare to a combined budget for example.

This is not possible, because the values are all coming from different data models so are not available as a combined value in a single report to pin to the dashboard.

It would be very useful to have a new dashboard tile type (similar to the concept of visual calculations in reports) to be able to combine and perform calculations on multiple dashboard tiles with similar data types.

For example, a new calculated tile D = tile A + tile B + tile C

or new calculated tile G = tile E / tile F