I remember there is some functionality like this already but it changed over time and I think you also worked on this code. In what state is this functionality right now?

Most likely you are referring to #2530 however it still is based on last-seen (and it actually breaks specification a bit); mentioned there ExtendedPresenceProcessorIfc applies only to outgoing presence.

If memory servers me right the idea behind this was to allow seeing last offline presence of our buddies, even after we reconnect.

Ok, so we still need to work on this. I remember that either this particular field or another one similar is/was used to optimize presence traffic, so if a user has more than 1 connection, the second connection does not need to query all the contacts for their presence.