I think we'll see a trailer in December based on when it's going to be released and the information that has been shared. There was a Fiscal Year projection from Square that came out, maybe it was on the FFVIIRemake reddit, it states that there is an expected increase of sales starting FY 2020, which FY 2020 starts in Japan April 1st 2019. The development cycles (when they are full production, not concept stages) for FFXII was 6 years, FFXIII 5 years, and FFXV 4 years. Considering they are no longer using their own problematic engines anymore and what was stated about the cutscenes being farther along than KH3 I'm guessing that part 1 will be released either December 2019 or early 2020. Unless it coming out at the end of 2020, which would go against their projection, I doubt they will wait until the next E3 to start hyping up the release.
Edit: I could see them showing something at Jump Festa which usually gets about 100k attendees each year. E3 was 70k which is the largest its been since 2005.
Honestly I want Square to take a page out of Capcom's book in terms of how they've handled the Resident Evil 2 remake. That's how you handle remaking a beloved entry in a long running franchise. You just let people know it's being made without the misleading tech demos stuff that FFVII Remake pulled with its E3 announcement and PSX trailer. Then once the game is ready to be released within a few months you show it off and give proper deadlines. Capcom did the right thing by not overhyping people by showing them a product that looked like it was ready to release in a few months, years before it actually was and that allowed people to keep their hype and expectations in check. What Square has done with FFVII Remake is create a situation for themselves where they simply can't win. Either the game comes out early and unfinished due to pressure from fans and investors like what happened with FFXV or it just simply doesn't live up to the hype once it does release on the intended schedule. Whatever happens Square has already doomed this game to not live up to its massive hype.
The first one is okay but it's very sparse as well. I think the second one does way better of a job. There's so much more detail in the scene. The first one is still admirable though, anyone who spends time to create anything is better than doing nothing at all.
I mentioned to someone in the reply underneath, that that specific slide is showing three things. The 1st thing is a Prerendered look dev pic, which is what that T-pose FF7R Cloud pic is of, the 2nd pic of the guy in the mocap suit next to that pic of FF7R Cloud is of a real time mocap preview, which is using UE4. The 3rd with the fireworks at Midgar is from a "real time VR Express" at the Square Enix Cafe. All three of those were shown in the Visual Works showreel video shown just prior to the slide, though the showreel itself is not included in the video so it just goes straight to the slide afterwards. So only the first two would have anything to do with FF7R itself, with the 1st one most likely just being look dev CG test for the prerendered CG Visual Works did itself.