There are basically two big things that I think make Morrigan possible, albeit somewhat unlikely:
1. We seem to get a traditional fighting game character during each wave of Smash DLC (
![Ryu :ultryu: :ultryu:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
for Smash for,
![Terry :ult_terry: :ult_terry:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
for FP1,
![Kazuya :ultkazuya: :ultkazuya:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
for FP2).
2. Our fighting game characters have, thus far, come exclusively from the golden age of Japanese arcade fighting games during the '90s.
This alone gives Morrigan a niche she could occupy. Darkstalkers is still a fondly remembered and influential classic of that era, especially in Japan. Being Capcom's other big fighting game franchise during that era certainly helps. Plus, Morrigan has a pretty unique moveset in terms of normals and potential mechanics that could be introduced and... other qualities that continue to make her incredibly popular 20+ years after Vampire Hunter/Saviour 2 was released.
That being said, Chun-Li, Sol, Scorpion, Nightmare, Nakoruru, a (dedicated) KoF character, and Kasumi could all theoretically occupy this spot as well, so I definitely agree she's not a shoe-in. Her being in competition with Capcom's stable is also a roadblock, but I have a hunch we'll get more than one Capcom character next game. There are just too many great choices to not double-dip.