Illusio
No words, only rage
I'd imagine if Ash gets a Mega, it's probably going to be Charizard. Sceptile could, but I have doubts on that considering it's not as big as the dragon in promotion.
While I wouldn't doubt it's popular, that's the first I've heard of it having a cult following there. Do you have any information supporting that?
Regardless, considering its big debut in Origins before it was even revealed, I don't think popularity was the big reason it's used so much.
We've seen Mega Charizard X twice because apparently it's got a cult following in Japan, so if Ash ever Mega Evolves his Charizard, it would become Mega Charizard X as well in my opinion.
While I wouldn't doubt it's popular, that's the first I've heard of it having a cult following there. Do you have any information supporting that?
Regardless, considering its big debut in Origins before it was even revealed, I don't think popularity was the big reason it's used so much.