Ethan dies after the prologue, is being replaced by Chris.
Ethan turns out to be a bioweapon himself. This would explain Chris' actions.
The guy can regen after all. He survived the Bakers incident. Mia turned out to have a sinister past. He's not a regular guy. He's too boring of a character to base another full game on. I really wonder if we play the entire thing with him.
They don’t even need to make a clone. It's not that crazy of a theory either. There are literally hundreds of surviving Wesker children from project Wesker all over the world, lorewise. The 13 that were given the virus that gave Wesker his abilities were just the most promising (though only Albert and Alex were the survivors). Alex wanted to infect them all to make more of her and Albert.
None of the Wesker children are related by blood though. They’re the product of a eugenics program helmed by Doctor Wesker (and Spencer) so they were all just given his surname. They’re all the genetic cream of the crop from their respective races, but without Alberts abilities (Alex survived the infection stage but didn’t get Alberts abilities because she had a degenerative condition; that’s why she transferred her subconscious into Natalia in Revelations).