I find I don't particularly like the idea of mystery cults or the RAW for initiations, yet I quite like some of the virtues they make available. I've been contemplating adding them to the list of Good Effects from Wizards' Twilight so they can only be gained during play rather than in character creation.
Have any of you ever experimented with this approach in a saga, or another alternative way of gaining these virtues?
Any thoughts or suggestions on making them available via Twilight experiences?
I think making them available via twilight makes sense. They are "mystical virtues" after all, and to gain virtues via twilight requires gaining a big chunk of extra warping so there is a balancing factor to it already. I think that you should maybe be careful about making sure they make thematic sense with the twilight experience and the character - but that's true of gaining non-mystery virtues that way too.
Another option is to do something with the magic realm xp rules in RoP:M. In the magic realm the "vis" you get instead of xp can be used to acquire virtues appropriate to what you were doing in the realm. Maybe you could make entrances to the magic realm more common, and questing for powers in the magic realm could take the place of mystery cults, at least partially?
Another solution is to treat the order of hermes as a mystery cult.
Think of it as an open mystery cult without much of the cultic aspects left. With initiations being based on some hermetic ability (have your pick of OoH lore, Magic theory or a new custom ability).
They would still be initiation scripts but treats the entire order of hermes as being a mystery cult that functions much along the lines of how house Verditius is treated in canon: A society of peers where initiating others into a specific mystery is seen as "simply something one can do" as opposed to treating the mysteries as a sort of ladder towards enlightenment as understood from some fringe perspective.
I like both Argentius and Euphemism's take on this.
Which Virtue to grant by twilight is already up to the SG and grating one that is normally part of a Mystery Cult (if it fits the Magi) is perfectly acceptable. I would even go so far as to say that many Mystery Cults are build around knowledge that was gained through twilight. This is perfectly acceptable as something that can be done by RAW.
As for treating the entire Order as an open mystery cult, that actually works well as a means of gaining Hermetic Virtues. If using this, I would recommend OoH Lore over Magic Theory, since that feels closer to the varies Mystery Cult Lores and adds increased importance to a lesser learned Ability rather than one which is already critical to Magi and studied in depth.
I would also recommend looking at the system in Apprentices specifically for teaching Hermetic Virtues (Apprentices, p.40). Apprentices system is derived from the Mystery cult system but focused on teaching rather than initiation. It uses (Com + Teaching +3 + other bonuses) against the same difficulty as Mystic Cult initiation. It has the same modifier from gaining Flaws (though it is changed from a reduction to the Target into a bonus to the Total). Granted it does not have a rolling bonus from taking a Flaw and gets an increased difficulty on total Hermetic Virtues possessed, but those can be addressed since you are already looking at a HR to in general get away from Mystery Cults.
Going the route from Apprentices feels closer to actually teaching Virtues. It does not allow self learning and the one teaching must have the Virtue being taught. HRing in a rolling Flaw modifier and the possibility of Initiation Scripts would help. It already includes a +3 from Time/Teaching, since it is a seasonal activity. Going this way still allows for the existence of Mystery Cults for people who still want them around.
You can easily include both of these and have them work together. Twilight allowing the gaining of the rare/nonexistent Virtues, which teaching allowing giving them to others.
Alternative solution is to take the same approach as Fortunata from the Legends of Hermes. She did not want to be constrained by the hierarchy and obligations of a Mystery Cult, but wanted the benefits of the mysteries.
Thus she devised her own Cult lore, and integrated as many ancient, lost cult lores as she could find. She then used this cult lore to self initiate into many Spirit Magic mysteries, and wrote books on the lore with the intention of spreading it among other magi; give them a new route to power with no obligations to any Mystery Cults.
What you could do is pursue her Mysteries, or follow in her footsteps and devise your own with a similar intention. Funny thing is; from many of these old Cult Lores she devised initiations into mysteries that require Hermetic Magic, despite many of these Cults predating Bonisagus and his Magic Theory. It seems to suggest that initiations are basically a way to "invent" some of these mystery virtues without going through the whole process of Original Research, though of course you should consult your Story Guide.