What status effects or mechanics would you like to see?

[Estellios]

I'd like to see Slow and Heavy be involved in mechanics the way Stun often is - for instance, if Slow reduced the "charge up" rate of a boss preparing his big instant kill so you can do damage enough to disable it, or if there were immortal mobs that chased certain players but had no Heavy resistance, meaning you need to kite them and Heavy to have time to do other things. However, due to the fact that no party can be guaranteed to have access to these, it's unlikely.

Both healers actually have access to Heavy/Heavy-like effects. WHM has Stone (I don't blame you if you forgot about it) and SCH's Miasma has Disease which also reduces movement speed.