We cannot provide an ETA, but it is definitely one of the top features that we will be adding soon. For what it's worth, you can now use calculated metrics to create views with different allocation settings. For example you can build a calculated metric called "Revenue Participation" which contains only the Revenue metric, but sets the allocation for revenue to "Participation." This is only intended as a short-term workaround, but it does accomplish the same thing.
Thanks Ben! I'll try that out and see how it works 🙂