This command, in my opinion, would be a great addition for creative Minecraft, or building. What the /freeze command would do is freeze literally everything, from the moving textures to all mobs, but only you can move. Other things the command could do is stop the day/night cycle, randomTickSpeed, weather, and mobs spawning.
This could be used if you just wanted a frozen scene with no mobs moving, no crops growing, no rain moving (sort of like a screenshot or photograph).
The command would be as follows: /freeze <seconds> or forever <thing to freeze> or all. An example would be: /freeze 20000 rain, cropGrowth, mobSpawn, textures.
It would also come with a counterpart, a /unfreeze command, which you just type to return everything back to its normal state.