I am in a Skyrim DLL modding discord that has pored over any footage of development tools. They have noticed that BGS are using a version of the Creation Kit for developing the game, so I think it’s basically guaranteed that it’s a version of the Creation Engine.
I think it’s not possible for them to make modding tools that are as powerful as DLL plug-ins like SKSE. While they can try to cover their bases with modding hooks, the reality is that they can’t think up everything that a modder might want to do and so DLL mods will still exist. And because DLL mods involve modifying the game code to do literally whatever (including potentially turning it into a completely different homebrew game, hacking the console, or even booting an OS), the problem with that and consoles is that the console makers do not want arbitrary, unsigned code to be running on their consoles.
No matter how many official hooks are added for modders to use, the PC platform will always have strictly more powerful mods.