I like the connection you made between the Shiekah and the original interlopers!
I briefly mentioned in one of my recent threads that I think that only a section of the supposed "dark interlopers" were sealed away! The name suggests that this section of the tribe were named the "dark interlopers" becuase they tried to overpower and enter the sacred realm using their dark powers (fused shadow) So the original tribe could have been called something much different!
In fact it mentions that the "Dark interlopers" are a tribe of sorcerers, so it could infact be that they are indeed many connections between multiple races in Hyrule in other Zelda games! I am going to make a thread about the interlopers and their connections in my next theory