[Sasky]

Not much has changed, really. Your options are pretty much:
A. Change each addon to use EVENT_SINGLE_SLOT_UPDATE the minimum it can. How this is implemented depends on the addon (some might be able to avoid using it at all).
B. Have them all use a common library that buffers the events to make sure it doesn't process too much at once.
C. Hooking would require loading an addon first then overriding the RegisterForEvent handler. The only way an addon can be guaranteed to load first is if all other addons depend on it. (So again, change each of the addons.)
D. Have ZOS implement some sort of fix for the event buffer and/or EVENT_SINGLE_SLOT_UPDATE. Note: this might require changing the API for that event, which would require changing each addon.
E. Don't use that many addons with EVENT_SINGLE_SLOT_UPDATE