Responding to these posts is getting a bit tedious and repetitive for me, so how about a thread for the old hands to conveniently collect the upgrades and improvements that have been made over the years, since I'm surely leaving out much of the smaller stuff like increased player cap and improving server stability and the like.

I'm feeling lazy, so I'm just gonna copy/paste my last reply on the subject.
Splitting NA and EU data centers, resulting in significant login capacity increase.
Adding four new servers to EU, significantly increasing active player cap.
And preparing to implement OCE data center, an unprecedented move to improve playability for an entire region of players, as well as significantly lightening the burden in other regions by spreading the load.

The last one is important because the planning and beginning stages for that happened way back last year, not so long after 5.0 launch. Which means they knew growth would require new hardware back then and began the process to address it with what they predicted would be sufficient. That process was expected to be completed by 6.0 launch. And it ran into delays.
The fact that they began this process so long ago should give you a pretty big hint where they might be on adding any more hardware anywhere else to deal with a population growth that began to exceed predictions and expectations. If OCE was predicted to alleviate congestion growing by old model expectations, nothing they could or would want to do to adjust to current models would've even been operational before 6.1 at best.

In short, the player population has been growing for years. And the infrastructure and hardware has also been growing at pace. But there's nothing they can do fast enough to react to that population growth massively accelerating. They're already hit with delays on one major project, any other upgrades or acquisitions will necessarily have to happen after that project is complete.
So, to the old guard, what other upgrades have definitely never happened?