This would make it possible to Wagneer a way to:
If "*all+*add metadata" existed, then when any card foo was added, the card creation form would include a second section beneath the card editor and above the Submit/Cancel buttons, for which "*all+*add metadata" would be the form (much like +*content).
"+*edit metadata" would also be available, analogously to +*add help and +*edit help
This metadata section and its fields would be differentiable with CSS selectors, and probably have a different default look.
+discussed in support tickets
+relevant user stories