Has anyone tasted these two great tastes together? It seems to me like a perfect match -- Gloranthan cultures already have keys and secrets (just not so formalized), cults obviously provide their own secrets, etc.
It sounds like a perfect match.
Grab a culture and GO!
The thought occurred to me too as soon as I playtested TSOY. I think that converting material from HQ would be very easy. I think that TSOY fits tighter, more individual-focused Glorantha campaigns like a pint on a berserkers hand.
What I'd do is, restrict most of the secrets to cults with liberal conversion of affinities, feats, secrets and such to TSOY-secrets and to a lesser extent; abilities. Then I would restrict the number of keys a character can have to 3. The players could choose additional keys if their characters were initiated etc.
It would be quite easy to make it happen.