I also find the expansion on Order of the Eagle being aligned with Tilea and Knights of the Blazing Sun being aligned with Estalia to be interesting, because this is something that could be inferred from 2nd Edition. In 2nd Edition, the Knights of the Blazing Sun have a chapterhouse in Talabecland where they keep an overland route open for pilgrimage from the Empire to Magritta, which of course incenses the Tilean Myrmidians who view Remas as the centre of Myrmidian worship. The Order of the Eagle on the other hand, is led by this guy in canon, Lorenzo Di Marco, the Eagle of the North:
"For most Myrmidians, the posting of Eagle of the North is seen as a banishment. Living amongst the brutish and superstitious northerners in their cold and depressing country is not something most Tileans would ask for. However, Lorenzo di Marco is not most Tileans—for he does not see banishment, he sees potential.
The current Eagle of the North is an insanely ambitious man. He plans an expansion of Myrmidian worship unlike anything seen before. He looks to the Empire and sees a troubled people who need new guidance. Sigmar has proven too weak to keep Chaos at bay, and his cult is rife with divisions. Ulric has proven to be too brutal, and is unacceptable to the increasingly urbane middle classes. Myrmidia, di Marco knows, is the perfect answer to the Empire's problems.
Of course, the Ulricans and Sigmarites are already moving against this threat, but di Marco is a tactician, and this is a campaign he has planned for a long time. As far as he is concerned, there is a new war brewing amongst the cults, and it is a war he does not intend to lose." Page 45 Tome of Salvation
Order of the Eagle are situated in Nuln and are primarily in charge of furthering the spread of Myrmidian worship in all its forms, whereas the Knights of the Blazing Sun are a famous and reliable Knightly Order who spread the word of Myrmidia through action. The Orders of the Righteous Spear are a number of smaller Knightly Orders under the control of the Eagles across the Empire, having an incredibly wide but shallow coverage of the Empire. Blazing Sun are not under the direct control of the Eagles, which irks Lorenzo. It's a complicated political situation, but I don't think it's quite started to escalate to any notable levels by DL's current time.