Being a fan of both Karna & the Pandavas. Here's my take on how Mahabharata story would have been if Karna truth was out. Here Kunti tells about Karna sometime after the Lakshagraha incident as she can't forget about the rangabhoomi at all and does not want her sons to kill each other. Also I won't keep too many episodes and try to finish it in 10-12 episodes
To tell some of what I have planned - Karna will fight the Mahabharata war with Pandavas and become ruler of Hastinapura and also a daanveer as well
Episode 1: The truth is out
After escaping from the Lakshagraha and reaching the Hidimb forest and Bhima's marriage to Hidimba, now Kunti can't help forget about her 1st born son - Karna whom she got from Lord Surya. The rangabhoomi incident, which happened some years ago, still keeps haunting her and even after trying so hard, Kunti keeps on getting nightmares. Kunti was thinking of telling the truth, but somehow she could never gather enough courage to tell it to Karna or to the Pandavas
Now in the peaceful environment of the Hidimb forest, Kunti finally decides to tell about Karna to the Pandavas. The 5 Pandavas are all sitting together and enjoying food when Kunti calls them. Yudhisthir asks - "Mata, what happened". They all see Kunti having a totally different expression, which none of them had seen before. Arjun asks - "Mata, why are u looking so tense. Is there anything u want to tell us"
Kunti says "Putra Arjun". She stops while saying and finally manages to tell the Pandavas that today I am going to tell u about my past. U all would be knowing about how I took care of Sage Durvasa when I was a teenager and how he gave me a magical mantra due to which all of u were born. But there is something more to it. "What" - the 5 Pandavas now ask. Kunti, is struggling to say, but finally she manages to say that "U all have a elder brother as well whom I got from Lord Surya". The Pandavas now look astonished as to what their mother just said. But the cool & calm Yudhisthir asks "Who is our elder brother, where is he. And why did u never tell us about him earlier".
Now Kunti says to Yudhisthir that "I was worried about what the public will think and what the people of Hastinapur will think, that's why I wanted to keep this as a secret but when he came in front of my eyes that day, my past started to haunt me and give me sleepless nights, that's why I want to tell about him to u all and feel peaceful from inside". Yudhisthir says "This was not a paap, but rather a punya as he is a divine blessing of Lord Surya, but you insulted Lord Surya by never telling about our elder brother to our father Pandu, who would have accepted him whole heartedly". Now all Pandavas ask "But mother, where is he now, where did u saw him". Kunti, is again struggling to say, but finally she says "That day in the rangabhoomi, I finally saw him after so many years. He is none other than Karna, the son of Lord Surya"
All the Pandavas look stunned now, especially Arjun. Yudhisthir, has the courage to ask further and asks Kunti, why didn't she tell during the rangabhoomi or immediately afterwards. And Kunti replies by saying that she was scared that what Samrat Dhritarashtra, Mahamahim Bheeshma and others will think. What the public of Hastinapur will think that I have a son before marriage. Bhima looks surprised as he can't forget how he insulted Karna at the rangabhoomi. Both Arjun & Bhima feel bad for their bad words to their elder brother that day
The 5 Pandavas now realise that Duryodhan would have crowned Karna as Angraj only for his personal benefit on some wicked advice from Mamashree Shakuni and that Duryodhan will only use Karna for his personal benefit. The 5 Pandavas, now decide to keep this as a secret and decide that they will tell about this to their elder brother Karna at a appropriate time as they are currently "dead" in the eyes of the world after the Lakshagraha incident and don't want to appear outside