I've been wondering about it for a while and since it came up in the 0.14.1RC5 discussion I was reminded of it.
So why not just save it like all the other scripts and simply load as with the ship's window where you can see the formation? Like this it would be possible for mods to extend it.
The script would be a collection of named-formation lists of positions. It would define the lead ship position as [0,0] and all others in relation to it plus maybe heading rotation. And maybe assign a "weight" (not mass) to each position so ships can be sorted by cost or size for placement. The lead ship (and or others?) can be an exception to the rule, though. This would allow something like an escort formation with one or many protected ships.