this sounds like Fei and Long Long from the Miraculous Ladybug Shanghai special and Longg from Miraculous Ladybug proper are all eligible characters, yes? and probably so are other ML characters (original or otherwise) who (like Fei) have access to the Prodigious dragon transformation or who (like both characters above who were named by mispronouncing the same bit of Mandarin) are dragon spirits of magical objects?

but Ryuko, Dragonbug, and other characters using the Dragon Miraculous are not eligible in themselves, since they're not turning into dragons? (though there's a past Cat Miraculous wielder design, of dubious canonicity on account of other past Miraculous wielder designs by this person have appeared in season 5, in which he turns into a magical lion, so if a Dragon Miraculous wielder were to turn into a magical dragon instead of a human with dragon-inspired magical armor, that sounds like it would be eligible?)