For offline use, since the underlying mobile geodatabases are SQLite databases, this functionality is inherently "available." That said, how this would be implemented would be opening a giant can of worms for the developers. Somehow being able to add database triggers to the mobile geodatabases would be an answer. We mostly function offline, so I have not investigated what is "under the hood" for online maps in use - but if it is different, then the rules/triggers would also need to be applied at the service level when an add to a related table is submitted - and updates would also need to fire the correct trigger. Regardless, the interface to add these triggers would have to be at the service level.
Currently, we allow our users to update the parent feature and then create the related table records overnight using the Python API. This gives the user the visual effect they are looking for, and the historical information is created overnight. The biggest limitation here is that you are limited to one update between script runs and you need to track how to find these updates via date fields or through other calculated fields in the form(s.) Users editing multiple features, since this does not enforce the forms or calculated values, is another obstacle if they are allowed to edit multiple features.
Another option using dynamic joins, which I have yet to test, was also passed along to me:
I hope this helps. (Sorry if you saw this twice - I wanted to add it under a different account.)
Mitchell Grafstein, Horticultural Inspector 1, NYS Dept. of Agriculture and Markets
