Add a Cooldown on Shifter

Avoid meta has set NLs far above and beyond all other classes in any meaningful bossing situation, in addition to a slew of other things. Shifter contributes to a good chunk of NL dodge rate. Avoid/shifter also makes for a much more efficient shadower sed mule.

What if we added a 15 second cooldown on shifter? Cooldown duration can be adjusted, of course. What if shifter cooldown could be reduced or reset by entering into dark sight?

A flat nerf on Shifter would be unfair and unwarranted to active Shadowers, but if going into dark sight resets your cooldown, it would create a utility gap between active Shadowers and sed mules.

Thoughts?