Would like to have Justicar's Vengeance as part of the rotation. I think its left out because it uses 5 Holy power. But its one of the strongest strikes It seems like a wasted talent if it's not included.

It's left out because nobody takes it, really. When you sim, you don't even cast it right now.

In the meantime, refer to the Wiki/FAQ if you'd like to add the ability to your priority.

If you want to do some testing with SimC and find a scenario where using Justicar's Vengeance is a DPS increase at all, provide those sims and I'll look at incorporating it. The theorycrafting crowd have found it to be a DPS loss to even bother with it.