I think he could be a World Champion again; I just feel that it is unlikely at the moment due to the booking direction on RAW. The main event right now is a land of the giants and comes with the looming spectre of a fourth attempt to make Roman Reigns the standard bearer for the company.
Indeed, if it did not seem that Vince was so set on getting Reigns established, the Miz with his mic skills, character and the Miztourage (which could include Elias) would be a perfect act to take the title from Reigns through shenanigans over the summer. At the very least, Miz could and perhaps should be Roman's first non-Brock, non-Braun feud over the title.
I would be far more confident of a second Miz World Title reign if he was on Smackdown, where he would make a strong challenger for AJ Styles.
The other issue potentially blocking Miz getting a World Title again is that he has two records within his 2018 grasp surrounding the Intercontinental title - Chris Jericho's most reigns of 9; Miz currently has 7 and most combined days holding the title - on a total of 523 days, Miz is only (a WWE recognised) 96 days behind the 619 day record of Pedro Morales.
With record-breaking/equaling reigns the likes of Punk, Cena, New Day and Nikki Bella all getting considerable WWE focus, it would not be surprising for Miz to be kept away from the World Title to accommodate more records.