From my experience I have an idea to make the interface system more dynamic in PVP/PVE. More dynamic, more players are going to buy runescape account.
Have the Health Bar across the Ability Interface. That way it is much more easier to see and instead of squinting at the small bar on the left side of the interface where its located.
Maybe you can have potions and prayers have timers on the top of the screen, like in the Witcher 2.
That way we can know when our anti-poisons run out or how long a certain prayer lasts, for example. It takes a lot of time out of going through the interfaces to know. If more players buy runescape account, Jagex can spend money to improve the system so I hope Jagex can earn a lot from selling runescape accounts. Free version is for fun.
And this generation is fast so it'll highly help out.