If I recall correctly, the Disperse Build and the Disperse Reclaim suggestions were denied, because it would be too overpowered and would increase the skill gap between players who are using and not using these features by several astronomical units.
The other player can not easily equalize this with just a few more actions per minute when he is not using, for example, spread attack key, when he wants to target multiple units
The game is already hard enough to learn for new players, adding more features that are necessary to learn and to master will possibly result in a decrease in new players and more frustrating moments in game experience.
At least, I would like to test those features, because I would like to see how it changes the dynamic gameplay.
Maybe the balancing team can finalize things up.
Edit: It was denied because of the possibility of abusing those features via UI mods as well.