This is a pretty interesting approach.

We've been doing a similar pattern already, because we have our web app iframed and communicating with outlook (via Office.JS) and gmail (via InboxSDK.JS) in order to read changes to the To: field and insert contents into the compose page based on that:

* stimulus encapsulates the javascript logic that "bridges" to Outlook and Gmail, including initializing the To: field listener * stimulus actions can trigger the "bridge" as well

It's worked out very well - though I really hate dealing with native stuff in general - especially compatibility nightmares with older versions of Outlook. Probably less of a problem with iOS/Android.