Sorry we didn’t officially announce this.
The Soulforge was adjusted earlier this year so that mythics are now selected from a pool of troops that is only reset once it is empty. This ensures that we rotate through all troops evenly. At 4 troops per week it takes about 7 weeks to empty the pool and start again.
For further details on these changes you can read more about sampling without replacement here:
https://www.ma.utexas.edu/users/parker/sampling/repl.htm
Based off of some historical data, we know what is still in the pool. We can therefore be certain that some troops will appear within a time range, before the pool resets, but otherwise we have no control or knowledge of what specific mythics will appear.