It would just need to put mud, jungle grass, and any stone or dirt in the vicinity of it in the list of do not corrupt.We can't save the jungle because:
1. It would take to much time for make an "anti-evil algorithm to protect stone and grass on jungle from being corrupted"
2. It would take too much hotfixes
3. The jungle is generated on a mid-corner of the world, the same place where hallow and the evil biomes are generated on hardmode.
Npcs on evil biomes would be nice, and maybe even evil biomes exclusive npcs.
More potion? Of course, this would make corruption be equalized with crimson (crimson have more contend and it's harder than corruption)