An icon will show when you reach a certain break point for haste/spellpower at which it is no longer worth to cast Mind Blast. Taken from the Shadow Priest Discord using calculations done by @Linelo.
Let me know if you think something is off with the numbers or if you find a bug
You can use this WA to replace your Passion's Mind Blast Tracker: https://wago.io/7st1SUTWG
Check out my other WeakAuras: https://wago.io/p/The Dude