Admins at WikiA have full delete rights at WikiB, even if they are non-admins and explicitly blocked at WikiB!
As I understand this feature in no way would give deletion rights of WikiA at WikiB, they would still delete the file only at WikiA, regardless of the interface they use.
I understand that you qualified your statement with "If I'm an admin on that
remote wiki...", but I don't see how that can be done without explicitly requiring a username/password each time a user wants to delete (plus, you are then giving your remote details to the local wiki sysadmin - an unscrupulous sysadmin or maybe even a badly behaved extension would be able to access these).
Shouldn't single login (minus username conflicts), allow such identification?
Bence