Arnorian successor states? 3 or more

[Belegorn]

Good point about the Istari Ixnay. I think that the kingdoms of the two younger brothers [of Cardolan, and Rhudaur] are pointed out as the greater of the lesser realms [those being Arthedain, Cardolan, and Rhudaur] as Gondor [line of Anárion] was greater than Arnor even though Arnor [line of Isildur] was the state of the elder line. Arthedain [line of Amlaith] was the kingdom of the elder line as well, but the younger lines appeared to have the greater power, though probably not so great as Gondor to Arnor.

It is clear that aside from the House of the Kings, there were other princes [like in Gondor]. After the line of Kings died out in the kingdoms of the younger brothers, in Cordolan there was still a prince until 1409 which is at least 53 years after the last kings there perished.

Take a look at the map and the borders of the three kingdoms in Eriador. Could some smaller realm exist there where Arnor used to be along with those 3 kingdoms? Would they have branched out into territory previously not held by the lords of Arnor?