It will also be interesting to see at least one song with lyrics by Mangini but I don't think it will happen, if it does I will be very happy.
Would love to see that happening, but, sadly, it would only create more MP vs MM arguments
A more likely scenario is JP co-producing with JR. That seems more likely to me, and would probably achieve a better, more balanced sonic production, just from having two points of view in the room rather than one.
That's the route I thought they would take when Portnoy left. It made sense because Jordan is the one who is always using the latest software and technology to achieve better sounds, so definitely he knows a thing or two about producing an album, since he also produces his own stuff, but no, JP decided to produce all the albums by himself, instead.
We're already 3 albums in and this hasn't happened, so I really doubt it will. However, I do remember an Jordan saying it would be cool to work with an external producer when he was asked about it on an interview (couldn't find the link), but that was around 2013, before DT12 was out, so It doesn't seem like it'll happen anytime soon