I'm considering the following variant for Star Wars Rebellion (inspired by Twilight Imperium):
Resolve space combat entirely and reconcile transport capacity before resolving a ground combat in a system. Note that this rule does not apply to ground units that are moved to the system by abilities that ignore transport restrictions (such as "Lead the Strike Team").
The effect of this is that the attacker must win the space battle and not lose their transports in order to attack a system. So, for example, the Empire can't destroy the rebel base by running in with a single Assault Carrier loaded with two AT-AT's (I have seen at least one game won this way), but instead must actually beat all of their forces (space and then ground) in the system. It also makes destroying capital ships more valuable in space combat as this gives the extra opportunity to destroy troops before they land.
What in the game breaks with this variant?