There's a whole lot of back-and-forth in this thread, and a lot of it is incorrect. Since I can't sleep, I'm going to try and point out some things.
Let's start with this.
Bethesda game mods are not some magic programming wizardry. They are simply databases - think of a really big Excel spreadsheet. The "master" (ESM) file is simply one big database with each in-game object, NPC, etc., having its own reference number. All a mod (ESP) file does, basically, is say "replace reference XYZ with this new information" or adds new information to the big database.
Making a video game modifiable like Bethesda has done is not inherently difficult - they are just one of the first developers to see a lot of success with it. You need only look at other games that support modding communities (such as the ARMA series or Minecraft) to see that other game developers have done the same thing. Valve games (like TF2) are known for it as well (hats!).
"No other engine can do with this engine does"? Sorry, but that's not true.
Let's first look at what the Fallout / Elder Scrolls series are perhaps best known for: sweeping worlds that extend out to the horizon. There are many different game engines that have accomplished this feat, both old and new. And, no, Fallout 4 does not have the biggest map size, not even close. Just Cause 3, running on the Avalanche Engine, has a map size of 400mi2, much more than Fallout 4's 43mi2.
And as far as "hundreds, even thousands, of fully interactive objects" in the game world, let's clarify some things. Bethesda games are made up of cells, roughly 3317.76 m2 in size, and the number of cells depends on the game in question. For example Skyrim has roughly 11,186 cells. Without getting too technical, Bethesda games load everything that's in the current cell the player is occupying, plus or minus a few things (such as buildings that are set as view-from-distance). Obviously the game does not load every cell, with every object in that cell, or else your Xbox One and PS4 (and most PCs) would beg for mercy. The cells (at least in Skyrim) with the most "interactive" objects are often interior cells - think of all the knick-knacks scattered on shelves and tables that you can Fus Ro Dah everywhere. At most you're going to get 400-500 different "interactive" objects. And I put "interactive" in quotes because these objects are simply physics / Havok enabled, i.e. they can be bounced around by the physics engine and put into the player's inventory. Doing that sort of physics work is nothing new (see Psi Ops: The Mindgate Conspiracy for a 2004 example).
So the supposed "feat" of having hundreds / thousands of "interactive" objects in the game-world isn't something that only the Creation Engine can do, since it's not some marvelous thing.
I think I saved the best for last. The "human eye critical limit is 24 FPS" is completely wrong. The flicker fusion threshold (see https://en.wikipedia.org/wiki/Flicker_fusion_threshold#Explanation)) for human eyes (specifically the cones of the retina) have a threshold of 60 Hz (though at very high illumination levels). What this means is that most people are able to detect intermittent light flashes up to 60 Hz, and after that the light simply appears to be continuously on.
Personally I don't really see the need for a brand-new engine, but there are definitely some issues in FO4 that I hope Bethesda fixes.
And one more thing: tying your game physics to graphical frame-rate is a bad idea, even in the indie game-dev scene where we play around with programmer graphics all day.