I have seen a fair number of posts about /friends on skyblock and economy, and as such was wondering if this plugin could be added to classic skyblock as well. There are quite a few people who exclusively play on classic, some of which I know for certain would appreciate this command. I don't know if this is possible with the plugin, but it could be interesting to have it show which server your friends are currently playing on as well. If this plugin is incompatible with classic I fully understand that, but I couldn't see the harm of suggesting this, arguably minor, change.
I understand this could be a problem, at least for cross server activity. However back when i had a small server I did stumble upon some friend plugins for these older versions of minecraft, though I am not sure how the EULA change has affected them. Implementation is fully up to the devs, and as mentioned before, if it is not possible due to version mismatching I understand this and will not pursue the matter further.
There use to be like a system like in /classic where you can do /friends and there will be a UI that pops up. But right now i'm not sure and haven't used it for awhile. And what Monster said /classic being in 1.8 maybe cause some problems.
Neither /friends nor /friend are recognized as commands on /classic, I do in fact remember there being something like this on there now that you have mentioned it. All the more reason to possibly look into adding it.