Not going to spend too much time on this idea at the moment, but the basics I have thought about. Things could be too straight-forward and boring?
There are Melee (Attack), Ranged, and Magic... With the combat triangle (Melee is effective against Ranged, Ranged against Magic, Magic against Melee.) Bosses will not have a style-weakness (probably), and might sometimes do typeless damage(?)
I would think about separating it so each style has their own Level number, but I suppose using the same level number could work....
There are many tiers of weapons/equipment... in which you must be at that level or more to wear... 1, 10, 20, 30, 40, 50, 60, 70, 75, 80, 85, 90, 92.... etc.
The higher the tier, the harder it is to obtain (Hopefully)... so level 1 bronze equipment could be a common drop for low tier enemies and such... Where as a level 92 could be a very rare boss drop (from a repeatable boss) that you also have to manipulate in some (rather expensive?) ways to be able to use (Maybe something like the Forge in Yallam? And/or something similar to whatever RS does?), plus, they'd degrade.
--- Er... idea has been cut short for now, but could add more later. - As a small disclaimer, I never said that this was any more than an idea, so whether a hack would eventually be made is unknown, and not likely at /this/ current moment.