The way promoting posts works reminds me immediately about “Proof of Burn” concept.
You send some assets to an account that is locked forever. This way you prove you invested resources to promote your content.
Since @null account has been already created for this purpose I think it is worth to think about out other uses cases for this account. What comes to my mind are:
1. Burning unclaimed assets.
Some users post contest or articles written by someone else and they state that SBD earned by the post will be split between author and winner or original author.
What if original author does not want the reward or the contest is not resolved?
SBD is still earned so maybe the part of it that can’t be distributed according to initial intentions could be burned via @null account? This way post authors look trusworthy and noone would blame them for claming whole earnings for themselves.
2. Carbon voting, voice staking.
There was a dispute in Ethereum universe not so long ago whether to fork ETH or not. A site http://carbonvote.com/ has been published and people could send ETH to “Yes” address or “No” address expressing their opinion. Ethereum developer Alex van de Sande created a MIST application (special Ethereum Mist browser application - DAPP) https://github.com/alexvandesande/stake-voice as a tool for creating such referendums when you look your voting assets for some time.
Steemit @null account could be used in a similar way but with a difference that assets used are burned forever therefore such voting could have much bigger meaning.
3. Additional reputation/awareness mechanism.
One could send a significant amount to @null account just to get awareness of his actions (example bitcoin transaction with huge fee didn’t go unnotice (https://blockchain.info/tx/cc455ae816e6cdafdb58d54e35d4f46d860047458eacf1c7405dc634631c570d) or to use it as a reputation improving mechanism. Openbazaar uses this concept: https://blog.openbazaar.org/why-proof-of-burn/
What do you guys think? Can @null account have interesting uses cases other than content promoting? Let me know in the comments.