They said that true DX12 compatibility had no ETA, so I doubt it's in this patch. However with performance improvements, I believe there was some things about reducing the amount of server calculations, but I could be wrong.
Yeah I also would like to know what are those "performance improvements", because implementing login queues can also be considered as such.
To seriously reduce server side calculations game would need complete overhaul, especially group calculations since we have the most issues on trials and groups in Cyrodiil. Problem lies in exponential growth of calculations per group member. Maybe simplyfing logic gates in calculations could improve efficiency of algorithms, but this could lead to some unpredictable results in such complexed code. This is not an easy task.
"We are currently investigating connection issues some players are having on the European megaservers. We will update as new information becomes available."
— They always claim they’re “investigating” the causes, but in reality they’re just waiting until the PC EU players go to bed. Once that happens, you can suddenly log in again and they happily mark the issue as Fixed.