I can confirm that this isn't being planned to add in the game as of now, at least there were no "official" talks of implementing such a feature in 5.0 or in any near future.
Last time it was suggested to make slight changes to fighter models or start positions a year ago we got a "no-no" answer from hampa.


Even if it's going to be implemented, I'm 99.9% sure that it'll only be supported by new mods that will be optimized for these stances and all the mods we have now will stay as they are.