There are a lot of other reasons for all these HD remasters we've been getting lately.
One reason is that they're cheap and fast to make and can be used to help disguise these droughts we've been experiencing as we wait for brand new AAA titles. They allow publishers to put something out on store shelves every year.
Another reason could be that some of these HD remasters didn't perform well last generation because console and software sales were on a decline. They came out during the death march. They came out during a time where people experienced all that they could with last generation consoles and were moving on to other things.
Another reason is to establish that user base, which I think is what you're suggesting. I can agree with this but I see it as establishing the Final Fantasy fan base in general and not something that's really specific like the world of Ivalice.
That said...
When you look at Square Enix's E315 line-up this year, it was pretty packed. Instead of jam packing everything for one event, they probably thought it would be best to space things out. I kinda feel bad for some of Square Enix's other offerings because once that FFVII remake announcement was made, it overshadowed everything else. That shadow would have grown bigger and darker if FFXV had a big presence. World of Final Fantasy you say? What's that?
I doubt a FFXII HD Remaster will be cheap to make. Not only does the game have a vast number of locations compared to both FFX and FFX-2 combined, it also has the most ornate and meticulously detailed art direction of any Final Fantasy. Assuming the development team don't cut corners, it would probably be one of the most tasking HD Remasters to make. Even in Square Enix's situation, they don't really have any release window space to release it right now. They have a crowded schedule through til Q2 2016, which means a FFXII HD Remaster would have to be released sometime after that. FFXV is likely a Q3/Q4 2016 release, meaning FFXII HD Remaster would have to be even after
that. We're looking at 2017 release at the earliest.
FFXII HD Remaster needed to be made more than FFX|X-2 HD Remaster for the sales reason you mention. Seeing as Square Enix saw to do otherwise, I'm further lead to believe they're holding on FFXII for a specific reason, which is the Producer/Director of the game being busy with another project. Even back at E3 2013, Kitase said in an interview with RPGSite that FFXII was the most deserving game for a HD Remaster, but he couldn't speak anymore on the matter because he didn't work on the original game. In another interview by Eurogamer in early 2014, he further clarified by saying whether a FFXII HD Remaster happens or not is fully dependant on the team that made FFXII, and he has not heard any plans about them doing it. This interview was published on the exact same day I met Kitase in London for the European launch of LRFFXIII, and he told me Ito has his own development team in Square Enix and busy on his own projects, which is why he has been absent from AAA titles since FFXII. It all adds up. FFXII HD is being held back because of Ito is busy on whatever the fuck he's been working on for the past decade.
Also, establishing the fanbase on current gen is a definite reason for these HD Remasters. Shinji Hashimoto even said at the China PS4 press event that they plan to make every mainline Final Fantasy (besides MMOs) available on the platform, so everybody in China that owns a PS4 has access to all the numbered FF games.
Lastly, I'm in full agreement that their line-up this year was bloated, but I think that was a good thing. It showed that Square Enix was still gaming force to be reckoned with and had not fallen off like some people claim. That the FFVII Remake announcement stole the show alongside Shenmue III, which shows there's still love for Final Fantasy. If there was a FFXII HD Remaster and a FFXVI by Ito announcement to add to that, it would have been complete overkill. That being said, I honestly doubt FFXII HD will be announced this year. Not after that packed E3 lineup. My realist self is expecting it to be announced alongside FFXVI by Ito, whenever that will be.
Alternatively, there's the window seat. When a veteran disappears for the better part of a decade without resurfacing once (as a company will shuffle idle staff to other projects, even if it's only in a supervisory capacity), there's a good chance that something is wrong.
It's correct that as a Final Fantasy producer, there's no going back. Hiroyuki Ito has his own team (even if it's one person) and the right to lead a new project. However, that doesn't necessarily mean that he's doing anything besides endless proposals that will never be approved. As of now, we can only confirm that he writes proposals, loves to challenge new things, puts together plans, etc.
The window seat is still a possibility, but my evidence points to otherwise. The man is definitely working on something. It's just that what it actually is he's making is on some highly classified, CIA-level shit. No idea why that's the case, but the secrecy surrounding the title makes me believe it's highly ambitious in nature.
I think that proposal statement by Shinji Hashimoto only cements how Ito is working on something big. Hashimoto said he's making proposals, not a single proposal, but
proposals for the project. On just one project, he's making multiple proposals of what he wants to achieve. This indicates he's trying to accomplish many different goals with this one title. Hashimoto even added that it would take time for this project to materialise because of how much depth Ito was adding to the gameplay systems and mechanics. Also, he even said he was excited to see Ito's ideas soon. The game can't be stuck in the planning stage if the Final Fantasy Brand Manager is excited to see Ito's ideas.
Further more, Hashimoto said something similar to me when I did a follow up report based on his replies in that interview. I met him at the KH I.5 ReMIX European launch event in September 2013, around 2 months after this interview was published, and I made sure ask about Ito. He said that Ito's been busy planning his own project, which is why he hasn't worked on any FFXIII games, FFXIV ARR, and FFXV. I then asked when this project will be announced, to which he replied that Ito was adding a huge amount of depth to the gameplay systems and mechanics, meaning development of this project would take some time. He ended by saying I should please be patient while awaiting more details. By the sounds of it, the game is already in dev, but the scale and ambition of it has it being made at a glacial pace. Ito's already gone on record to say PS3/Xbox 360 couldn't handle his ideas for the next evolution of ATB. I'm starting to think PS4/Xbox One can't handle it either.