Well, I'm leaving tomorrow morning and the timeline and stats aren't done yet, but I'd might as well put up a little preview of the map, and a (very) short summary of the timeline so far:
The PoD occurs in 281 BC. In the spring of 281, Seleucus Nicator was within reach of capturing the throne of Thrace and Macedonia, in addition to his own Syrian kingdom. At the request of Lysandra, the wife of Agathocles (the son and heir of Lysimachus, who was disinherited and killed by his father in a dynastic intrigue), Seleucus had invaded Lysimachus' holdings in Asia Minor; and, having killed Lysimachus in battle and destroyed his army, there was nothing standing between Seleucus and Macedonia itself.
In OTL, Ptolemy Keraunos (Lysandra's brother and disinherited son of Ptolemy Soter of Egypt) assassinated Seleucus near Lysimachia in 281 BC, having realized that Seleucus did not intend to restore Lysandra to the Macedonian throne, but to take it for himself.
My timeline raises the question of how the world would have developed if Seleucus had not been killed at Lysimachia. I justify this by having Seleucus be a little more politically adept than he was in OTL; he makes it clear to everyone that he will in fact restore Lysandra, and this he does. Reaching Macedonia, Seleucus puts an end to the kingdom of Lysimachos, and captures the Macedonian-Thracian throne. Rathen than take it for himself, he makes a subtler power play: marrying his son and heir Antiochus to Lysandra, and appointing Lysandra as Regent of Macedonia until after his death, when Antiochus will reach his majority as king of both Syria and Macedonia.
With Europe secure, and Ptolemy Keraunos satisfied with Seleucus' sincerity following the restoration of Lysandra, Keraunos and Seleucus launch a campaign to overthrow Ptolemy II Philadelphus (Keraunos' brother) in Egypt. This campaign succeeds, and Keraunos is restored to his throne in Egypt.
Seleucus dies a short while later of old age, and is succeeded in Asia and Europe by Antiochus. Antiochus and Lysandra have several children, who intermarry with the children of Ptolemy III Keraunos; when all is said and done, a dynastic union, not an outright reconquest, has reunited the empire of Alexander.
That's as far as I've developed the timeline in detail so far. What will happen is that the Greco-Bactrian kingdom will rise in power with a series of successful campaigns in India, and will ultimately seize Medes from the "Seleucids" (I need to think of a better name). The "Seleucids" get involved in the Roman (Punic) Wars on the side of Carthage, securing Carthaginian victory in the Second Roman War (Second Punic). Carthage ultimately sacks Rome itself in the Third Roman War, causing the administrative center of the Roman state to shift north to Aquileia (may change it to Ravenna). Carthage becomes the dominant power in the West; East and Southeast Asia develop very much like OTL, the only differences being some minor effects in Southeast Asia caused by Bactrian power in India (including some interesting, IMHO, religious differences).
Whether Kalthzar is going to mod it or not, I intend to post the comleted timeline and map when they're finished.
Map as it currently stands, c. 100 BC:
http://www.civfanatics.net/uploads10/reunited_alexandrian_empire_map4.png
EDIT: Removed image tags to make the text easier to read