I've never had the blockchain in my home but it is still sustainable to run a consensus node on a consumer grade PC (like the workstation I'm using to write it).
Non-linear growth is an issue, but your equation is wrong, we have bandwidth constraints (which should be more strict IMHO).
Most important question for a witness:
Why did not you "hard fork" to delete zeartul, bellyrub, bellyrubbank in time, and returned their stolen property to their victims?
That's not related to the witnesses at all. If you chose to send someone your STEEM, or SBD then it's up to you. You have the right to be wrong.
Steem has a firm commitment to property rights, no hard forking change that reduces a user’s existing account balance of Steem, Steem Dollars, or Steem Power will be allowed. These balances may only be changed as the result of an operation signed by the account holder(s).
- Steem Constitution (Draft) by @dan