1.25 is bringing a fairly major change to how blocks textures are handled.
In 1.24, blocks texture is a game-wide setting that applies to all the worlds. In 1.25, each world will have their own blocks texture assigned. The global setting is gone. The same mechanic applies to character skins.
When you upload the world, the blocks texture and character skin will be packed together with it, so that whoever downloads it, will get them automatically.
This is a long planned change that unfortunately took a very long time to do, due to unforeseen troubles :-(
Anyway, it will allow you to create adventure worlds with associated block textures and skins. Let me give you a silly example: you will be able to create a basketball court with pumpkins turned into basketballs, trapdoors into hoops (by use of blocks texture), and player made into Magic Johnson (using character skin), and have it all working just by selecting the world. No need to search for, download and select blocks textures and character skins.
Here’s how the new World Options screen looks like:
Hope it all makes sense :-)