The only issue I see with the way the High Arts are handled (at least the ones that only have Rituals) is that there isn't a way to "initiate into" the art. The way I understand it, in order to learn Necromancy (for example) is to "spend" your initiation learning that art. In the process you learn the first ritual of that art (Grave Binding for Necromancy). From then on, you are able to learn the other rituals of that art as per the normal ritual learning process.
The way it is currently handled, every magician who initiates even just once has access to all of the rituals of Geomancy, Necromancy, Divination, and Invocation. Plus they can still choose a metamagic. I don't believe that was the intention, and that particular aspect is not answered in the responses from Jason Hardy.
In the mean time, I did some quick scripting and made up "Metamagics" for the arts of Geomancy, Necromancy, Divination, and Invocation. This allows the user to Initiate and select one of these four arts and it automatically gives the character the appropriate ritual:
Geomancy: Aspect Mana Line
Necromancy: Grave Binding
Divination: Augury and Sortilege
Invocation: (defaults to) Summon Great Form Spirit, but there is a drop-down box that allows you to select Ally Conjuration instead.
*These new metamagics have the Source of "Ritual-only Arts are selectable as Metamagics" which I set to be listed under Street Grimoire Optional Rules
*I am not truly sure this is the correct interpretation, just what I interpreted. As such, I provide this user file as an option to those that agree with this interpretation.
*Technically, this file does not change the mechanics as they currently exist in HeroLab, I did not want to risk making something that would alter the mechanics for these rituals. These changes simply give the user a way to "select" one of these arts specifically. It does not prevent purchasing the ritual if you have simply initiated.