Not sure if you've seen this yet, but I thought it might be of interest to you regarding Thorn's Mystara. Zomp's Sylvan Realm
post (taken from one of the Dragonlord books), seems to indicate that there was a Blackmoorian installation not more than 4 days north of the Sylvan Realm.
So if that's the case, then why would Ilsundal (a rabid anti-technologist) choose to create his new "Returnist" home so close to the taint of Blackmoor? I'm starting to think that maybe Ilsundal had an ulterior motive to the formation of the Sylvan Realm. What if he established his nation of anti-technologist elves right at that location specifically to keep an eye on the ancient citadel and to make sure that no one ever breached its walls? And what would this mean with the coming of Moorcroft? The name has some similarities to Blackmoor Craft. So perhaps Moorcroft is actually a student of ancient Blackmoor, who wishes to bring its technology (or whatever is trapped within the citadel) back into the world.
Just some thoughts.
Thorn's Mystara canon (if there can be such a thing) states that Moorcroft was one of the most powerful demon-assisted magic users. With Zomp's information above, I wouldn't put it past the demon to have invaded the Sylvan Realm in order to wipe out the last guardians of the Blackmoorian outpost.
We know Illsundal created the Tree of Life in the Sylvan Realm, but where did he get the final pieces of knowledge that he needed to complete his task? Strange, that it should be after the elves settle in the Sylvan Realm, so close to the Blackmoorian outpost. Wouldn't it be ironic, for the leader of the Returnists to have relied on Blackmoorian magitech to complete his work and ascend to Immortality?
Trees of Life are capable of halting the Wasting, driving out demonic possession, and harm demons coming near them, whether they be in material or etherial form.
Hmm... what other device do we know of that does something similar?
Could the Blackmoorian outpost known nowadays as Dragon's Watch be the seat of Andahar's Engine?
If it is, it makes Moorcroft's destruction and occupation of the Sylvan Realm all the more disturbing, and Illodius' pursuit of the last clan back to Alfheim an ominous turn of events.