That would be cool, force players to maintain supply lines to make it so their units don't get debuffs, or maybe take attrition damage. This would heavily nerf the armored car going wild on enemy land tactic that honestly is a hassle to deal with without similar mobility or aircraft.

No sorry gentlemen, this sounds like an easy way out...the opponent is too difficult to handle so let's penalize him.
I understand the supply lines argument and the game works on the dot and line system,if players feel that can't work because they're "cut off" then yes but should the game be close to reality, shouldn't it also be realistic that cut off units can be supplied? I also understand that cut off units must sooner or later surrender because they cut off and they shouldn't heal and be supplied but should this happen,I suggest a new aircraft unit,a supply drop plane.Cities can also be cut off and should then also be penalized because of no supply line.And what about health booster cards?If my cut off units are being penalized to not heal what will be the use of those cards,will they be penalized again after I used it?
And I know most players don't use paratroopers but their use are for dropping behind enemy lines being cut off.Technically there's no rule or law that says paratroopers must only drop onto cities,they can be dropped anywhere on the map, every player has their reasons and strategy why and where they drop them and they will be cut off.
Runaway stacks are a pain in the rear but also should those cut off stacks decide to go back to it's provinces,they will have to fight their way through enemy stacks that surrounds them and they can be taken out.
This is a strategy game.If a turd fell into your drinking water,adjust your strategy.
I stand to be corrected.

Cool idea, cool points, but idea's been discussed to death. At this point, it is fully in the dev's hands whether to implement such a system; no input from the community wud make a significant difference.

I've been on the forums for a lot longer than you have mate, and I can count the number of times on one hand how effective non-bug related suggestions have been implemented due to pressure from the forums. Ask any vet about how the RRG nerf was implemented; they'll explain. And that is just a balance issue they fixed. Imagine how much of an outcry is necessary for completely new features, like the whole "supply lines" feature yall are suggesting.

Btw, I ain't dissuading yall. Make as mant suggestions as yall like. But just remember; the chances of these actually getting implemented is close to nil.

I would really like something though…