I am currently ironing out these topics.
XP System. I am working on an xp system that I feel is better than what was presented. Its still a work in progress though.
Training/weighted clothing- creating rules on armor. Its near completion
Knockback- This one is fun. It is practically done, but if you look at the rules for knockback as they exist today, they are quite clunky. I am using a simplified way of figuring knockback. More on this soon.
Challenging Opponents- I am working on how to better design encounters without leaving players in the dust.