Matt's role has had no confirmation.
I think some have surmised that Matt won't be there on the basis that Neil said, during his podcast, that he looks forward to working with Nick.
Meanwhile...I suppose you could say Matt's silence is deafening but, at the same time, I don't think he's one to really stay afloat on social networking media. I remember, after Intriguer, some had speculated he was out of the band because of how quiet he is on Social Media.
Until you hear otherwise, Matt is still in the band and he's been silent many a time before now.