I've played AOE4 (during the free load balance trial), and sure, it's not Age of Empires Online, that doesn't mean it's an AOE game (another example: Halo 4 and 5 may be called Halo games, it doesn't mean they are ones). This view extends to the group of friends I play AOE2 with, so while I'm glad AOE4 has found its audience (so maybe they'll redo AOE1), I'm cynical that any sequels will be ones we want to play.

The issue for the new DEs/4 isn't that they're proprietary, it's they've gone backwards for cross-platform play (no MacOS, worse on wine), hence the open source implementation (with propriety assets) would enable playing on whatever systems people have.

EDIT: I will agree that 0AD isn't the same as AOE2 if I want to play AOE2, but given the option of playing a game that will work (0AD) vs. one that may work (new AOM), I'll take the one that will work.