I rather think Mike Portnoy was the one who went in with preconceptions of what people would "accept" on a DT album, and I think BCSL suffered for it. ADToE sort of restated their identity - largely out of necessity - but I think all bets are off from here on out.
I'm going to have to disagree with you yet again.
https://www.mikeportnoy.com/forum/m2352022.aspx"In the end, JP and I discussed it and he just couldn't hang with the cookie...he thought it was just TOO radical for DT fans to swallow... "
Assuming that Mike is faithfully reporting here the discussions as they occurred, it is clear that Mike was trying to test the boundaries of what people would "accept" on a DT album (as you put it), and that John was the one to shoot it down in the name of what DT fans would "swallow."
And I agree with Perpeptual Change, for the most part, in this conversation. In my judgement, it is clear from ADTOE and DT12 that Mike was for the most part right about John's attitude towards these things. Those two albums are at least mostly safe.
They're also difficult albums for me, as I've said before. There are a number of songs on both albums that I really love, including OTBOA, FFH, BAI, TBP and IT. These are all quite simply among the band's best songs. But the albums on which they appeared were largely safe, largely in keeping with what is expected of Dream Theater. I'm not prepared to judge them negatively as albums for that, since that can often be good and I really do love the albums. But I definitely don't feel like nothing is off the table. I mean, yeah, there is the string/ambient section in IT, but the fact is that they did similar things in TCOT, 8VM and the overture of SDOIT. Same deal with some of the electronic stuff on BMUBD and Outcry—it first cropped up in ITNOG.
Again, this is not necessarily a condemnation of the albums, it is just an expression of my view that there's certainly a lot that is, in fact, off the table. I don't expect the band to ever really surprise us again, at least not more than the string section in IT was a surprise. I don't expect to hear another moment where I think "hey, they never tried anything at all like this before this album!" I do on all the pre-ADTOE albums (examples, working backwards: Day After Day, POW rap, 8VM intro, Vacant, SDOIT overture, TDOE ragtime, Chapman Stick on NM, SDV, sax on AD, WDADU was the debut). Meanwhile there's not been anything like this on ADOTE (electronic stuff can be heard on ITNOG, BAI surprised me by how good it was—and it's now my very favorite—but not with any new elements of the sound) or DT12 (ambientish/symphonic stuff they've done in the past, and The Embracing Circle, FAS and the BTV intro are really the only things that make a bit of a claim to being new sound elements).
It's hard for me to be exacting or harsh in this because I love ADTOE and DT12. They're fantastic albums, the both of them. But they don't excite me as much as the albums with Mike Portnoy. Not only do I prefer the feel of the band with Portnoy's drumming, but I also feel like each album with Mike went out of its way to be unique within the catalog and bring a certain sound characteristic of that album. If you asked, I could describe the sound of each of the albums and do so pretty specifically. Even
Black Clouds & Silver Linings, which is accused of being "generic DT," stands apart to my ear. I'd call it the most gothic Dream Theater album, and one that is extraordinarily evocative of the image described in its title. It's also the last DT album (in terms of most recent) that I love without reservation.
To conclude this very long post, I'll reiterate my agreement with Perpetual Change. The last two DT albums sound homogenous to me where the ten that preceded them each stand apart from the others to me. I will add that I understand that Mike is probably gone forever and that we're not getting him back, that I'm okay with this, and that I'm happy with Mike Mangini as the best choice of replacement. And I'm okay if we get like five more albums like ADTOE and DT12 because they have very good songwriting and, though they don't excite me as much as the first ten, they are in all honesty very good albums.