Yes it is great to have more support for related tables within the web viewer of ArcGIS Online, but what would be really great is to have the ability to
1). TO RETAIN FULL FUNCTIONALITY during the upgrade process of AGOL
a). everytime there is an upgrade to the AGOL platform, my organizations experiences issues with account/user permissions not functioning correctly. Web maps that are shared with no one displays on devices, accounts with full permissions to web maps and associated dervices lose the ability to download web maps.
2). Collector app support related tables
3). Collector app the ability to edit related tables
4). FGDB Domains manager that would allow for updating or deletion of domains or associated codes and descriptions.
5). Keep the labeling bug when downloading maps; that is a great feature to have...
Otherwise, I the collector app is great.