What if the next tour is Mangini-era heavy?
It SHOULD be. I'm not even a huge fan of the output of this era, and even I would support that. Dream Theater needs to maintain its relevance. The only way to do that is to very carefully balance how they tour and what they play. I think DT has always been extremely savvy in this regard. Frankly, I was surprised they relented and did an anniversary tour of I&W. But given perhaps that they swung the pendulum so far one way with the last album, it was necessary (both creatively, and financially) to do so.
But yeah, from here on, I really do think they need to be heavy on the Mangini-era of the band. DT has gotten itself into a bit of a spot because of the length of its songs. But I would say, they should probably shelve ALL I&W material for the next couple of album cycle tours (and of course WDADU), and perhaps just play a track from Awake, none from FII, and then play a song or two from SFAM-Black Clouds, and the rest of the set should be Mangini era tunes.
To be relevant, you need to support your new music, and let it become classic with fans. That doesn't mean that you ignore your past, but you don't dwell on it. A very, very fine balance, that up until the last tour or so, DT was very good at doing. I suspect, and I expect they will get back to walking that tightrope masterfully on the next tour.