Hmm not the first time charizard has appeared, he appeared in be an arrow. Return maybe??
But to an earlier comment that I forgot to and cant be bothered to quote, I agree with your seviper theroy. I mean It might not happen but if they were to bring a serviper back, why not let it be Jesse's, especially with the upcoming plot!!!
(Thank-you BW2 for realising that more universal pokemon needs to be used for sustained anime sucess)