Consider this, an M1A1 Abrams Tank can accurately fire a depleted uranium anti-tank shell at a range of more than two kilometers. This is something you never see main direct fire combat units do in any RTS game for the sake of balancing them with the very low ranges of infantry weapons. But Supreme Commander doesn't have infantry.
So, what would it do to the game if, let's say a m1 striker had a maximum range of 2 kilometers and all other land direct fire and artillery units had their ranges adjusted proportionally?
I think it would add a lot of strategy to the game and shake things up quite a bit.
Terrain would play a MUCH bigger factor and ambushes would be a much more viable tactic.
Artillery would play a larger role. (Did you know that most combat casualties in World War 2 were from indirect fire?)
Assuming you didn't significantly increase radar range then you would need to build and upgrade radar more quickly.
Larger maps would have more relevancy because of increased distances and wiggle room.
Shielded firebases would be perhaps more resilient because if units had to cross more open ground to reach them then driving under the shield dome to knock out the shield generator would be more costly because the swarming units would be under fire for a longer period of time.
5x5 maps would never be played in such a mod because if you can be sniping with t1 arty in the first few minutes then it makes the game kind of pointless.
Air would be a much trickier thing to balance because in reality airplanes are very good at countermeasuring long distance missiles.
I'm not saying I would always enjoy a long distance mod but since it's something you rarely see in RTS's and because in a lot of ways Supreme Commander sets the bar pretty high for plausibility, it's fun to think about.