actually, there is one potential dragon quest character i could see maybe getting in if they want a character that encompasses more than just one game.
Estark is the lord of hell and a recurring boss since Dragon Quest 4, appearing in tons of games afterwards, including spin-offs, and was even added into Dragon Quest 8's 3DS remake as a bonus boss fight. He's considered one of the first super bosses in jrpg history, and as you might be able to tell by his many appearances, is quite popular with the fanbase in Japan.
I don't think Estark will ever happen because like, he's a super boss that nobody outside of Japan super cares about, but his appearances do count towards something. He's a pretty unique boss too, he's incredibly powerful but keeps falling asleep during the fight. In Dragon Quest Heroes 2 he actually gets buffed when he wakes up.
i was planning on writing a thing on him so lol, i guess i got him on the mind. there's tons of other popular dragon quest characters that could potentially get in too