I've seen it mentioned by somebody around, and it's indeed a very anticipated feature. Trying to devise formations you may need with some team during pre-match setup formation phase in the limited time span is pain in the hind, it really is. And such formations will very likely differ for different your teams of the same race, as well, thus you may need to create a lot of them, and edit them on regular basis. Having a formation editor tool you could use between matches to prepare it all in advance would be of great help. There should be button on the Team Roster window presenting you with simple schema of the pitch, and allowing you to drag'n'drop your players' icons on it, thus outlying a formation, with an option to save it after that with a custom name.
If I also may suggest (in case it's implemented). There should be one global list of saved formations, and a separate list for each your team (not just race! so for 2 Dark Elves teams you could have different lists of formations). Let's call the global list "Formation Templates". Thus you save some general formations to "Templates", and then while populating list of formations of a new team, you can either create a totally new formation, and save it for this team only (or both for this team and pushing it into "Templates" as well), or you can import one from "Templates" and customize it a bit to match this team's build. The editor should also allow to directly import formation(s) from any your other team, not just from "Templates" (or at least allow to export it first from other team to "Templates"). Also should allow to remove and edit existing formations in any list.
And having some way to export/import it from/to the game itself (preferably in some human-readable format) to share with other coaches would be a blast.
It also should map player's number on the roster to a specific position in the formation scheme, so substitutions could be done more easily and you wouldn't need to change position of some players each time during setup on the field. Like, if Blitzer #2 is killed, you buy another one, and put him at #2 position in your roster. And you don't need to change anything else, he'll be put at the same spots in all existing formations at which the old blitzer would be placed.