For sure still Luminous or are you guessing?
100% it's still Luminous, they integrated the Luminous team into the FFXV team to speed up the development progress of both projects in tandem with one another. As
@Bionicle8563 mentions, they are using Umbra, but it's simply a C++ library that can be integrated into any engine. However, they also mention this...
The main reason why their version of Luminous heavily edited being that they probably won't continue using it so they didn't mind picking it apart and putting it back together.
This is completely false, it's not a "heavily edited" version of the engine by any means. In programming, you keep our code bases separated by many means. They exist in separate repositories and separate branches as well for development when testing new features or creating stable builds etc. The engine is no exception, there was a modified branch of the Luminous engine that contained some of its features that was actually integrated into FFXIV.
FFXV's codebase relies on the Luminous engine, yes, but it's not a "heavily edited" version of Luminous that can no longer be used in the future, that's simply not how you would structure a project, that would lead to horrible spaghetti code that would become completely unmanageable. Considering they have pumped out a few demos already, this is proof that they are using revisioning software (either SVN or GIT) and are able to create separate branches of the game and the engine for these one off demos.
The reason KHIII wasn't going to use Luminous anymore was because Versus became XV and was going to use Luminous, and it required a lot more time and work than they likely anticipated. Plus, with KHIII needing to go into full production ASAP, they couldn't wait for the team to finish working on the engine. Plus, the engine team is now working along side the XV team to speed up the development of both the engine and the game allowing everyone to easily talk to one another and request things in the engine etc.
As much as many people like to make fun of Luminous engine, the team are very proud of it (as they should be), it's by far one of the most impressive engines to date, and in terms of real time lighting and other effects, it's by far the most impressive most notably on consoles. The reason that they keep showing up at all these events for lighting and graphics like SIGGRAPH is because they are extremely proud of what they've accomplished and want to show off their technology. Famitsu (I think?) has run several articles of their engine developers going into great detail on many elements of the engine, unfortunately it's all in Japanese, but I believe
@Rin or someone else has translated a few of them, but I don't remember who/what/where honestly.
See, that's sort of what I was thinking, that GI misunderstood the Umbra thing and thought it was using a different engine entirely. I just haven't seen much discussion about it since that GI thing. Generally that'd mean there was nothing real to talk about, but I figured if anyone would know, it'd be someone here.
Yes, this is correct. Umbra isn't an engine, it's a C++ SDK, commonly categorized as "middleware" much like YEBIS which is currently being used for FFXV as well for postfx. Umbra is a bit like a tool in the toolbox, it's not the entire toolbox itself I suppose if that analogy makes sense.