The wither scorpion would be a wither-style scorpion that only spawns in the new soulsand valley biome, in the nether.
The size of the regular wither scorpion would be similar to the size of a regular spider. It would be hostile to every other type of mob except wither skeletons or any other wither type mob, and they would attack using the sting in its tail, poisoning you, so the only way to fight them effectively is by using a shield.
Every soulsand valley would have at least one scorpion hole, with lots of wither scorpions spawning inside, and at the bottom of the hole, it would be a Wither Scorpion Queen(or some other name), which would be a giant wither scorpion boss with prominent claws and sting, which would be used to catch the players and poison them. The Wither Scorpion Queen would be asleep, and the boss fight would start if you get too close to it or if you hit it. When you get to kill it, it drops his giant sting, which could be kept as a trophy(like the ender dragon egg), or maybe have some utility.