Agreed! I saw this mentioned in another thread (probably by you, theplottwist!) when I was lurking and the idea stuck with me. For the 'Legend of Christopher' to still be relevant we know that Soleiyu couldn't fight and defeat Dracula, but having him fight Elizabeth Bartley is a great idea - she is a significant character in the Castlevania mythos whose backstory hasn't been explored and the real life Elisabeth Bathory was active around the same time in history (her death following imprisonment was in 1614).
In fact, not only real world coincides with that, but the Bloodlines manual actually gives the "early 17th century" spiel about her death, and says that she was revived in 1914, 300 years after her death. So not only she's the one and the same, but Soleiyu was alive and well by the time of her death - right on his prime to fight using the whip.
Then, Elizabeth revives and JUST BY COINCIDENCE attacks Eric's lover, Eric himself having Belmont blood.
Elizabeth is established to have a connection to Dracula and to have lived in the late 1500s and early 1600s, so it's absolutelly not a stretch for her to be the one behind the events of The Adventure and Belmont's Revenge.
Making Soleiyu face against her gives her a reason to exact revenge on the Belmonts later. And since the Belmonts are gone, she goes for the next best thing, which are the Lecardes.
Soooooo... Are you listening, Konami? Eh, who I'm trying to fool