Ideally, I'd probably prefer just a 'spam tax' of say 30-50% up until Steem value is around 1, and then completely normal linear after that.
If the goal is to kill off the remaining steem user-base, then I would say that's a great idea. The average post payout is only a little more than 1 SBD (about 3 STEEM), but strongly skewed by the tiny percent of posts with high upvotes.
The median post payout is closer to $0.08, well below your 'spam' range. Calling the posts by more than 50% of all Steemians 'spam' would be a disaster.

Source: @arcange's Steem Statistics