Here’s one way it could play out: either third party services or personalized WoT relays create a big picture snapshot, with generic-ish trust scores for a huge number of pubkeys. This will require lots of raw data and lots of compute. So these are the scores that are in greatest need for recalculation and storage.
Next, we have trust scores that are highly contextual. The opposite of generic-ish. Like who are the experts in some narrow topic. These scores require less raw data, less compute and involve fewer pubkeys. So perhaps specialized apps could handle these calculations. The generic-ish trust scores could be accessed and used as filters so that the raw data used for contextual scores is not polluted by spam.
So two ends of a spectrum: generic trust scores calculated ahead of time with results made accessible for lots of purposes; versus highly contextual, specific trust scores that could be handled on the fly.
