Is there any way of baking some more user settings into the invite link, apart from group membership and topic_id? In particular, I would like to modify the frequency of the summary emails for some invites and setting some categories to watching or watching_first_post would also be great. Oh, and a custom message could also come in handy from time to time.
The reasoning behind this is the following: people are generally very reluctant to subscribe follow invite links because they are wary of getting even more emails. Explaining that discourse allows users to control exactly which emails they want to receive is too complicated so I would like to promise invitees something like "You will not receive any emails in you accept the invitation". Or "You will not receive any emails except those regarding XYZ". In order to be able to do that, I need to make sure that summary emails are turned off for those users.
This functionality would be particularly useful for diverse communities where categories constitute something like sub-forums and where people interested in one category may not be interested in another. In other words, you tell people: "never mind all the other stuff on the forum, we will only get what you want".