According to IMDB, Patrick Malahide is now listed as Magnus Crome on the Mortal Engines page. So, our initial speculation seems correct. Crome is a fascinating character, so I’m really looking forward to seeing him on screen. Patrick Malahide will be perfect for the role.
Hopefully there will soon be some production photos, but for now this artistic rendition from the Mortal Engines Wiki will suffice. 🙂