I'm loving the trendIts been 3-4 days at this time that aoe2 has more numbers than aoe4, so my guessing would be 6k players around late january or february.
In other numbers if you browse the ongoing matches for aoe4, they have lost half the numbers compared to 2 weeks ago, that is even more alarming cause those numbers reflect directly the actual MP numbers, right now aoe4 has only 300 games more running than aoe2, it used to be >1.5k so you figure it out.