Two improvement suggestions for the pop-up in Collector when using related features/tables.
Display Count of Field in Pop-up
This appears to work correctly in Map Viewer, but there's no count in the pop-up in Collector. Example of a count displayed on pop-up of the GlobalID Field:
Show Coded Domain Description in View List
When tapping on View in the Collector pop-up, the list of related records shows the pop-up title. However, if this title uses the attribute value of a field in the related object that uses a coded domain, the coded value is displayed instead of the description. It would be a lot more useful to see the description, rather than the coded value.
If you tap through to the specific related record, the coded domain's description is shown for the pop-up title (as expected).