I don't think you can make a property like this a trilogy. It's not Lord of the Rings. It'd be like making Paradise Lost a trilogy.
Have you ever read the poem? It's split into three parts. This film just deals with Inferno. That leaves them with Purgatorio and Paradiso for films 2 and 3.
So how do you turn it into a movie and actually make it watchable? I have read the poem. And it's not a poem you can adapt into a Pirates of the Caribbean type franchise.
Well the first movie is about Dante trying to save the woman he loves from Hell. That's a story that everyone can relate to.
And the poem involves Dante traveling through three fantastical worlds filled with supernatural creatures and beings and foes. That's perfect setting for a fantasy film.
But who says it needs to be a POTC type franchise? The poem isn't anything like POTC nor does a trilogy adapted from it need to be.
And this won't the first time Inferno has been put on film. Vincent Ward's What Dreams May Come which is based on Richard Matheson's book uses a lot of imagery and ideas from Inferno.