Quick update to the above. The “Labels to fields” transform I mentioned does now appear to also work for InfluxDB data (per my post here).
Unfortunately this doesn’t actually solve the issue, since the “labels” in “Labels to fields” need to come from a time-series database, and in the above example they don’t (that’s kind of the point).
It does appear that the missing piece is what’s described in this (currently open) issue: Support Graphing of Long (a.k.a. Tall) and Wide Format Time Series Dataframes · Issue #22219 · grafana/grafana · GitHub. I.e. what’s needed is the ability to obtain metric names from tabular data. For context, Grafana’s data frames documentation does a nice job of laying out the different possible data structures.