Apart from trading and pvp combat there are not many mechanically supported needs for player interaction which actually require presence of several players at one spot. Here I am to offer an idea how it could be changed little bit: druidic rites in a form of music.
- temporarily buffing or even permanently boosting quality of local resource nodes. Would require presence of, say, 9 characters with a set of different musical instruments, which ones exactly should be asked of the resource node with the help of low cost hearth magic, the answer should also contain the information of which tunes must be performed and in what order. Then they start playing each tune of the list for couple of seconds (or maybe even a chord). If the ritual done correctly, then the node receives buff for an hour (+5) or perma boost (+1) for the quality of the resource. Also may require certain moon phase and have significant cooldown.
- temporarily buffing stats of one character. Also requires presence of several players with the instruments (different setups for different stats) and playing of simple melody for a short time.
Oh, forgot to mention, each participant must have Druidic Rite skill, otherwise wouldn't work.
Of course all of this technically can be botted, but will take some time and effort. Please correct me if I'm wrong.