There are already STEEM based forks that works like that - user is given his staking-rewards once per day/week (depending on blockchain) and there is 99.9% spam free space.

The thing is that the same 99.9% of investors do not bother themselves by curating or posting anything. You will have another issue to solve - how to motivate people to do something else other than getting rewards.

Since those blockchains are spam free, the system force users to come and get their rewards daily / weekly or else they disappear.

Now we have illusion that blockchain is valuable because it is alive.