That would get in the way of Trevor's age (CVIII happens 6 years after Lisa's death), and Alucard must be around 14-16 or whatever around that time, so that in CVIII he is in his early twienties.
After looking back at LoI's story, the end of the credits states basically that the Belmonts will not face Mathias/Dracula for several centuries, as he's gone into hiding all over various countries. It sounds lazy, and Iga could've implemented many more interesting encounters with Mathias/Drac leading up to CVIII.
That little "lazy" bit of excuse for the Belmonts not to face him is actually really good for potential side stories:
A Belmont is in search for Mathias, keeping with his/her father/grandfather's promise to his former friend now foe that his family shall hunt him down. He/She will cross over various countries (similar to Bloodlines) in search of Mathias, coming empty handed each time. They shall eventually succeed, putting him to sleep for a century while human hatred slowly builds his power. He goes into hiding once revived, but in Transylvania, where the Belmonts have been exiled from due to their "superhuman" powers and strength, making a safe place for him to reside, building his new castle, Castlevania. Once the townspeople murder his beloved, however, he turns on them, forcing the church to call in a Belmont to save them, who's name is Trevor Belmont.
This unknown Belmont in search of Mathias can easily be Sonia, with a new love interest, whose motive for going against Mathias will be decided eventually (unless the story is revamped further).