You could use your plugins within custom code editor and map the values
to XDM schema to capture those values into platform and analytics etc.
Bonus point - Just to ensure that you upgrade your plugin code to the
latest versions as the legacy plugins might have dependency on
appMeasurement.js or etc.. to populate some values. That would solve the
problem for majority of them. Plugins are in Adobe pipeline to support
in the near future, the workaround helps in the interim to go ahead with
your im...