Mining serves two purposes:
1) reaching consensus on successive blocks of transactions
2) new coin distribution
Proof-of-stake can only serve the first purpose, which is why pure PoS coins are 100% premined by the coin creators.
Oh okay, So it can be done in other ways too? Like if wanted the miners to help in rendering a 3D model or Scene just like how renderpools work. Would that be an acceptable way as well?