Nope terrible idea. Dragboxes are important to quickly select a squad if you don't have the time to particullary select it. They've been a basic element of RTS for ages, changing this would be the wrong approach.
It's the design of certain factions that cause blobbing, not the basic tools that label a RTS game.
+ 1
There could be a very minor penalty for blobbing, Possibly if 3+ squads are grouped together they could take increased damage from enemy small arms fire since there are more bodies to hit.