The only reason why Tom and Elena would be the last in the petrova and Salvatore Doppelgänger bloodline is because Silas and amara died right so there would be no use for more?
Honestly never really understood that plot detail, I get the Petrova doppelgänger idea but always felt forced with the Salvatore doppelgänger. But yeah from what I can tell the Doppelgänger “spell” is broken.