When I was offered the Treaty of Brest-Litovsk with a small slice of Poland and some pocket money as reward, I decided to reject the offer and wait for unconditional surrender instead, hoping to gain a slice of the Baltic and access to Black Sea at least.
While the amusing "Your forces in the East have been infested by Bolshevism!" -event alone was worth the treaty rejection, I was surprised that in the end the new border ended up being drawn at the exact same place as it would have been if I had signed the treaty. Furthermore the states that would have been made independent under treaty remained part of Russia.
So I was left thinking it would be nice if rejecting the treaty had some effect on the outcome. Maybe the "border" could be drawn so that it included at least the port of Odessa so that Central Powers could transport forces from there to Ottoman Black Sea ports even if they otherwise lack access to Black Sea coast (if Bulgaria remains neutral for example). Also leaving the planned United Baltic Duchy to Germany would make sense.
Even with the treaty signed it seems odd that Central Powers lose access to Black Sea and Baltic even though Historically they occupied the territories until 1918.
Another thing about the Russian exit from the war, whether by treaty or surrender, it seems to go way too smoothly for the Germans.
In SC:WW1 the entire Central army in Russia is transported to German and Austro-Hungarian territory in what strikes me as the most impressive logistical miracle in the history of warfare. When Russia quits everything in the East is done and every single Central unit can be on the other fronts by the end of next turn. You don't need to leave a single unit East of Trieste or Frankfurt unless you are feeling really paranoid about surprise landing operations. I wonder if anyone has ever failed to do the "Ludendorf" with the Russian exit working as it currently does?
Historically, while the treaty did define the borders as they become in the game, Germany still occupied huge swathes of Western Russia from Narva to Rostov. While the Russian exit did release a lot of forces to the Western front, still a large amount remained tied to the occupation of Russian territories. Revolts and guerrillas were constant issue in the occupied areas that were already strained by the wars and revolution.
Maybe instead of War in the East simply ending, with the hypothetical future borders of the peace treaty coming into force, the historical occupied zone would remain under German control but with heavily reduced Supply and MPP production and large number of possible Partisan spawns. Furthermore if the Central player simply abandoned the occupation zone, there could be some NM reducing events for the Central Powers (communist ideas spreading to West with the troops etc). If the partisans were allowed to run amok too much they could even trigger some proper communist army that could even threaten the Eastern Germany and Austria-Hungary.
All this would make the late game far more interesting than the current unlimited transfer of Eastern Front troops to the West. It would make the Russia-first strategy less of a no-brainer and balancing with the number of troops tied in the East and the escalation of partisan warfare would be an interesting dynamic.
The amount of partisan spawn hexes in Russia makes me wonder if something like this was initially planned?
Since this extensive changes to the Russian exit are probably off the table, it would at least be nice if all of the Central units in the "abandoned" areas of Eastern front didn't make it to the West on the very next turn. Maybe the units could be stuck in transit randomly for 1 to 4 turns (like if they were on a off-map naval route)? This would make the end of war against Russia feel a bit more natural, although a proper power gamer would still probably operate most of their units out of Russia a turn before the surrender...