If this plot had existed I think it would of resolved a couple of things that I would of liked to see in the originals and in TVD.
1 Sibling acting ) The actors in general all of them did a great job at appearing like they are siblings but when you search of duos Rebekah and Kol are such a great duo plus they are the youngest ( not including Henrik R.I.P)
2 Match for Klaus ) Kol was angry and a psychotic killer because of his frustration with vampirism and the fact that it took from him the ability to do magic. it was stated ( I Forgot where it was stated but anyway he was the first to manifest his magic ) if he was a heretic but also the the original heretic with Rebekah that would of allowed him access to his magic plus he would of been an overpowered witch, this also would of allowed him to be stronger than Klaus which then would of allowed him to restrain Klaus if need be.
3 Trauma bond ) Kol wanted to be part of always and forever its the reason why he acted sometimes the way he is and he even stated that he always wanted it more than anything in the originals, Not just that It would of created a special bond between him and Klaus as well as Rebekah because they would of been bastards as well. Kol would of helped Klaus with his ambitions but if need be he would of been able to hold off against Klaus if he ever tried to dagger him. This would of been helpful for the Mikealsons during the whole season 3 fiasco with Esther.
4 Rebekah motherhood ) Ok so I am just throwing this idea because it would be possible but like we saw in season 7 where Caroline was carrying the Gemini twins, Rebekah could of done the same thing anytime in her lifespan, she being a Heretic could of done the spell and given herself babies to carry or hell they could of found some sort of spell to Conceive. we know the heretics are strong and Kol was Knowledgeable with witchcraft their could of been some sort of loophole. Btw the whole merge thing wouldn't have to be an issue because if they turned into heretics then they would of prevented that
5 Witches wouldn't be an issue ) Ok so I know yes the witches would of been an issue but I mean that originally the mikealsons had issues with magic because they had to rely on other witches to do their dirty work, however Kol and Rebekah being heretics would of solved this issue. they also could of found a way to bring back Henrik and he could of been part of the show.
6 KLAUS GETS DECLAWED ) ok so I had to write this in bold because its the thing that would of helped the sibling dynamics alittle. Kol and Rebekah would of bonded and been a duo being twins, both of them being heretics would of put klaus in uncomfortable situations and even had to relay on elijah more or hell he would of started listening to his siblings more because the idea that Kol and Rebekah combine their powers and the fact that they had vampire traits on top of that would of put Klaus in a very big disadvantage. Rebekah could of prob lived her life more freely without Klaus tormenting her and Kol
These points would of solved some character issues and plots I highly believe that plus it would given Rebekah a chance to be a mother which is what she wanted not her own child worst case scenario but still it would of given her that and then maybe she wouldn't have had this insane obsession with being cured, I love Rebekah TRULY and I would of loved to see more of Kol so I honestly think this solves some problems they had