The engine and server infrastructure (database - backend stuffs) are in desperate need of total overhaul.

This should be done before any other changes mentioned on this list are or even can be done so went with "other". Strong foundation first, build atop next.

Beginning with proper latency handling. For the love of the twelve this should have been addressed years ago. The way the engine responds to latency spikes makes gameplay feel downright awful terrible at the times.

Better character customization would already be more of the possible of model textures were not baked into armor (why you do this?!).