For what it’s worth to others waiting on this feature:
I have a database using Tap Forms for all of my students. I’ve added a field to use an Agenda URL Scheme to pull up the search of them (e.g. agenda://x-callback-url/open-search?query=@EzekielSonOfBalthazar). I’m not sure if I should be encoding the @ as %40 or if it makes a difference, but I’m not right now encountering any problems by putting it as an actual @ character.
The same idea could be achieved by a note. Obviously it wouldn’t auto-populate, but it’s a way to have a list of all your people. Even when Agenda does incorporate it natively, it’ll still be useful for me to have these links in my database.