This was my first thought, too. Maybe even a start for Philip, too, if the mechanics make it straightforward enough. They deserve the focus, frankly, so I'm perfectly alright with it not being there at base.
There is a one problem I see in all this that will make the time extending DLCs problematic. In CK2 the DLC added an entire age, for example the viking age. DLC adding a start date for some specific event may not be entirely viable. People tend to play the earliest date available to them, so a DLC let's say focused on Philip/Alexander would likely mean that any further addition of start date in a future DLC would likely break it, because earlier start would just make the probability of Macedonia's raise unlikely, thus depriving many people of the previously added content.
For this reason I am not so sure about the start dates for very specific events e.g. reign of Alexander, Battle of Thermopylae etc. If there is expansion in timeline it would probably have to be tied to something more substantial, like entirely different geopolitical situation in the world (Charlamagne) or significant religious difference (Old Gods).
Sadly reenacting specific battles and events is hard, when the slightest roll of random generator can annex countries decades before those events happen.
I am still quite curious to see how the late game is handled and if there is something that will give us historical figures like Julius Caesar. What if by the time his age comes I already dominated he world? What if I failed and am just a small blip in Italy? What if I became a tribal judaic theocracy led by a horse?
