This is the developing spec to look at and make suggestions on: http://docs.moodle.org/dev/Logging_2
Most (all?) of the "realtime" needs that we currently use logging for can in fact be moved in new tables for that purpose, making them very fast. That should free up the long-term logs to be huge and slow if they want to be.
Thanks Martin! I looked but hadn't found that page, must have been using the wrong search keywords.
I think my proposed system fits OK with the 'Logging 2' thing - i.e. it's an incremental step in that direction that can be implemented without hurting anything. Basically my proposal is the 'MUC-like plugins to interface between our logging calls and log backends' part of that page. It also fits in with the default (database logging) given on that page.
--sam