Currently, about the only thing you can do with friends is to hold private shiritori games. Since you can now do this with groups, it seems like there is an opportunity to retire the whole friend system altogether. Maybe this has always been the plan, and I am just slow to realize it.
One other friend legacy is the privacy settings for word notes and so on. The simplest thing to do with these would be to change the meaning of “share with my friends” to “share with my groups.”
Optionally, if you were willing to introduce new features, you could add the ability to restrict visibility to individual groups as opposed to all groups. It’s unclear to me whether there would be enough demand to justify the additional complexity.
Another causality of this action would be the friend-only rankings. I admit this seems like a non-trivial loss. Group-based rankings would only be a partial replacement.
Not planning on doing this - groups are *not* going to be friend groups, and will not be available for anyone to make (all groups must be approved). As they are larger groups focused around some learning topic, you'll still have (and do) small groups of friends playing shiritori games, accessing one another's lessons, etc.