you would have to prohibit all sand/red sand/gravel from being placed as well as prohibit all items from going into a llama storage...so again i reiterate the end being accessible is a bad idea unless your sole goal is to ruin the econ on the server

 

What archerexpert777 said. Block item entities, llamas, mules, and donkeys.
Why prohibit blocks getting placed?

 

Take a look at the nether, people are already farming the hell out of it and selling dozens of nether bricks for one grass. However look at quartz and blazerods (I think I haven't dealt with any blazes recently), they all have low chances of obtaining because they will flood the economy.

By using the same idea for The End, we can prohibit or lower the chances of elytras, red sand, gravel, purpur blocks (and its varients) because we know that they will hurt the economy.

Hope it makes more sense

The point of the end will be the same, just the items that will hurt the economy will have the chance of obtaining lowered, just like we did for nether quartz.