First ... fuck yes!!
Second ... do you really need users on your instance?
Third ... I know you mentioned staying away from custom feeds ... but would it be on the horizon to construct feeds of multiple lemmy/kbin communities into a single lemmy community? I don't know how useful that would be, but seeing the "News" feed you've got immediately made me think the same could be done for the various News communities that have been started around the fediverse.
Yes, people can subscribe to all the communities they like ... but drilling down into a single community is a good way to make sure you don't miss something if the content is important to you. Having a single meta-RSS-community for a bunch that you like could be really helpful.
Obviously you don't want to be in the business of allowing anyone to create their own custom feeds ... but I'm sure there are at least a few that many would appreciate.
Fourth ... fuck yes!