Lots of work went into performance / optimizations and most of the networking has been rewritten by now, at least anything concerning common packets. All numbers are with local connections, actual players might show different results but it should still be good to give a general idea. The local connections are paladins chanting every x seconds.
Last year around this time the server would flop over with 1500 connected or around 300 - 400 in visible range of each other, whichever happened first, playability for everyone started to get impacted at around half that.
Around February I did the first performance pass, after that it started to degrade after 3k connected or around 600 in visible range of each other and died with 3.5 connected or 700 in visible range. Since then a couple minor optimizations came that increased that by around 10% and in general all code changes since had performance in mind.
Earlier in November I did another performance / optimization pass with the goal to be lazy to avoid having to write a queue at all, with some intentional dynamic degradation based on connected player count, this starts to kick in at 3k connected and at first won't be noticeable but as more people connect the degradation will start to become noticeable, starting at around 5k connected it might start to impact rvr, pve should still be perfectly fine however but with a small yet noticeable delay.
The current maximum locally before it becomes unplayable is this:
We will likely launch with a soft cap that we can increase while the server is running to monitor the effects.
Another thing that impacted this but actually a lot more is getting things in a radius around some position, that's used super extensively as every active mob has to check for vicinity aggro, every ae spell has to get its targets, every action / effect / message has to be sent to players in a radius. That part is now around 10x - 50x faster than last year and no longer allocating at all.
