The Total Using functionality, which is described here and here, goes a long way towards addressing Jonathan Drummey's idea from 2012, Totals and subtotals over displayed marks instead of separate calc (aka make subtotals work like Excel).
In fact, perhaps the the current implementation of Total Using could be considered a reasonably sound implementation of Jonathan's idea. But alas, the Total Using options are not available for pills that compute across the data blend.
This idea is to extend the Total Using implementation all the way to completion. This includes pills that utilize values from a secondary data source. And if possible, perhaps even those that utilize an ATTR(). Column grand totals should be easy! This is especially true in the Enterprise business world that grew up on Excel.
For an in-depth review of the details behind this idea, as well as the rather gory workaround, please see my blog post