With all honesty, Ash should be replaced not by a Trainer that will start his journey. No, that would be boring if that is just like that. Ash should be replaced with this kind of guy, in my opinion:
The renowned member of Team Rocket, Alexander Black, (Also known as Black Flame) is the Boss' best bet in all the missions other Team Rocket members cannot handle. He is the Adam's favorite. (Giovanni's son, Adam, now rules Team Rocket, years after his death) He is considered to be stronger than any other members and possibly evenly matched with the Executives Giovanni has handpicked in his time. He is famous among everyone in the Team and considered to be a great threat among them. Alexander is serious in his work and does every mission bestowed upon him without hesitation for he has great confidence with his Pokemon. He is famous for his powerful main Pokemon, Arcanine. His teammate, Felix, is the only person Alexander truly trusts. He controls a Feraligatr as his main. The two have been close friends ever since they started training as a grunt. They built a friendship solid as rock that their Pokemon fights as one on the battlefield.
The evil inside Alexander starts to grow weak when he witnessed Adam dismissing one of his grunts because of a failed mission. Adam confiscated the grunt's Pokemon and cast him into the cold and unforgiving sea. The grunt adores Alexander very much but Alexander was helpless when Adam punished the grunt. He did not rebuked his Boss because he could not. He simply could not.
When the time came and Adam wanted to make Alexander a right hand Executive, Alexander refused and tried his very best to escape. But he was captured and his Arcanine was confiscated by Giovanni, he was thrown into the waters,beaten by the executives, and even Felix could not do anything to help his best friend.
After this, the story will start. Alexander will wake up without his memories and will go on a journey in order for him to know who he really is. (An old fisherman will find him, he will be the MOM's (Grandmother's) husband. He will be given a chance by the new life given to him. He will be haunted by his past through remembering small bits of his memories as the story goes and Felix would be one of his rivals because Team Rocket will soon know that Alexander survived. He will, of course, eventually discover his true identity but will fight his past and make something new out of his life.
Yes, I would love my character Alexander Black to replace Ash Ketchum. Why? Black is my character.
