Having challenges give some sort of tangible reward outside of the BP exp would be good. I definitely think they should be tied to the decay system as well in order to help determine active gameplay, when challenges are completed on a server. Like some have already reported, you get challenges done through normal gameplay. Having it needed to stave off decay would be a great resource to stave off refreshers.

The feature would have several controls available to server admins to determine how much decay is applied daily, how much of the bar can be filled at a time (maximum) and how much challenge exp applies (basically a multiplier). This way the amount of time that can be banked is determined by the server owner. If setup properly, normal players who play everyday won’t notice a difference.