Hi Gordon! Have you checked out the Definitive Editions of AoE1 and AoE2?
The custom scenario design scene is still active -- lots of old and new designers -- but has largely moved to other mediums -- such as reddit, the official forums, and discord. The official website is also the best place to post your creations and check out creations by other designers. AoE2: DE even comes with an in-game mod manager to upload, subscribe, and check out custom campaigns all within the game client.
I must warn you that the community is quite a bit quieter (and with less personalities!) than AoE/AoK Heaven were back in the days... not nearly as much discussion. But there's also a few YouTubers (especially Ornlu and T-West) who play custom campaigns on their channels and their discords also have lively custom campaign discussion from the player side... in short, the custom campaign scene has changed a lot since the early 2000s!
Congratulations on your retirement! Looking forward to what you create next!
(Great blast from the past on that thread you linked, Gordon! Funny to see 15 year old me on there singing praises to the Persian Wars after all these years -- I went on to become one of the designers for the Definitive Editions of Age of Empires I/II/III many years later -- think you and I may be the only ones still 'active' on that thread)
[This message has been edited by Filthydelphia (edited 12-19-2021 @ 08:00 PM).]