While they didn't get to summon Titan of their own accord (a developer would trigger it for them), they were told that summons each have different ways of being summoned and under certain conditions. Each of them is different and is not seemingly triggered by a "call anytime" button press. That said, they also stated that people can put aside their fears of worrying about them being like Episode Duscae. From what they gathered with the development team, it doesn't even seem like any of them are triggered from 0 HP on Noctis or anything like that (although, for one of the summons, it may be possible). It was also mentioned that there are at least 7 summons in the game (Carbuncle, Leviathan, Titan, and Ramuh, with hints at Shiva, Ifrit, and potentially Bahamut as well).
Those worried about the modern look of the game shouldn't fear: they saw plenty of concept art of later bits of the game and it is just as fantastical, whimsical, and extraordinary as we've come to expect with Final Fantasy. This includes monster designs.
Cities are all seemingly are on the scale of Novigrad, from Witcher III. In fact, they stated they are a little worried how filled these cities will be because of how big they are. Expect a lot of shops, alcoves, landmarks, etc.
Character interactions are important. Whether it be via the combat (like TC stated), the banter in the car, the animations in the field as they run around, or cutscenes where they are all together, how these characters interact and play off each other is a very core piece of the game.
The world is open, but shouldn't worry those who prefer more linear-based worlds. They described it as being (like many of us have stated) 1:1 interpretations of the old games' worlds. Just open enough to provide plenty of side stuff to do, but linear enough to focus on the main story and not get so sidetracked that it detracts from the focus.
For those who are fans of the pre-PS2 era, fear not. Many of the staff working on this game are fans of the older ones (as well as many having actually developed those older ones). V and VI were notable as being the largest influences. However, VII, VIII, and IX are definitely big inspirations as well.
Elemental magic is found via naturally occuring areas in the world, similar to FFVIII drawpoints.
Areas of Chapter 1 aren't chock full of tons of "goodies", but there is plenty of wildlife running around, NPCs every now and then, as well a couple handfuls of secret areas and landmarks to distract you if you want. It should also be noted, they highly emphasized, that Chapter 1 is in a desert area and is therefore somewhat purposely sparse compared to other segments of the game (it's also meant to be as an introduction). They pretty much said you will see just as much in the desert as you did in Episode Duscae.