And he received a new one for his lines in Bonds Beyond Time and Dark Side of Dimensions. I doubt either of Maddie's major characters (the other being GX's Sartorius) are out of the running. The only thing that makes me question Solomon is Yugi having an Exodia skill already.
They can easily find another voice actor. Other characters have different voice actors. Many do stay they same but that is not true for everyone. Character images for him, for good Bakura and for the good Marik have all been datamined. They are planned characters and it is most likely that they want to just hold off on adding him to give future content. Compare DM character list size to o/ worlds
Maddie was already recast as Sartorius in Duel Links so I don't see that being a problem. Honestly it would not surprise me if they're now saving Solomon for the supposed Filler World that's coming since one of his only duels in the anime was during the KCGP filler arc.