I am thinking of sinks for Steem and two come to mind.
Burn to Promote.
Burn to promote is the future of advertising.
Instead of buying votes, which leads to downvotes and is very complicated for new users, people can instead simply buy Steem and burn it for extra visibility on their content by pressing "promote". A way to easily promote posts has been proven to be desired as we have seen Steemians decline payout and buy votes for the post they want to get more attention on.
Example:
^ This user spent $90 to get this post to the top of trending, that isn't chump change.
Burn to promote creates demand for Steem and the burn creates a natural sink. As we get more users, the cost & demand of visibility within the platform will increase, and watch that circulating supply of Steem decrease and watch the price trend upwards!
For instance, on 3speak we are going to have ad slots where you can burn steem or SPK to pop your ad there. On 3speak we are also going to allow creators to use burn to promote on their tokenized Steem communities.
So if someone with a million users ports their community over, users can purchase the creators token, burn it, and get onto trending/ad space on said community. 3speak will buidl the tools for creators to leverage to maximize their profits on their individual attention economies.
I really believe tokenizing attention in a way people need to burn Steem to get extra visibility is such a great way to add utility leading to bullish buy pressure for Steem.
Whoever wants to make a PR for Steemit to have burn to promote (like 
Next Sink:
5% burn fee for Instant Powerdown.
While having inflation coming in, charging people to cash out early can offset a lot of the PoB Steem faucet we have. I also believe this will directly result in more liquidity and a higher market cap overall.
Investors with large capital will rarely "YOLO" into an investment (locking up Steem for 13 weeks with no way out = YOLO.) Since Steem has an actual use case, a lot of the stake is locked up and being used, either to power projects or for social influence, voting for witnesses, ETC. This creates very thin sell liquidity which leads to large buy orders never being filled.
Example: If I wanted to buy 10 million USD worth of Steem right now, I couldn't, it would take weeks/months of me setting buy orders and leaving my money on an exchanges for long periods. Large whales will say no thank you to that.
Sell liquidity is just as important as buy liquidity if we want a highly liquid token, so having a way to powerdown instantly, attaching a fee that is burned for the privilege will be a very good thing for Steem, IMO.
@Marki99 added a good point:
One truth about trading and investing: most people sell the bottom, most people buy the top.
This has to be true, cause otherwise there would be no pumps or crashes. When people buy at the top, it’s FOMO. When people sell the bottom, they are simply scared. At both times they act irrationally.
When steem pumps, it is possible to buy the top.
When steem dumps, it is impossible to sell the bottom, cause of the fucing powerdown period. We DON’T allow investors to be irrational.*
And if someone doesn’t sell the bottom, he starts a powerdown and continues selling at higher prices over weeks. We give sellers a better price. We don’t let them act irrationally.
We allow them to dollar cost average (selling not buying) and get better average prices over a longer period.
What this points to is the fact the price of Steem is artificially capped (either to the downside or upside.) While certainly, this is a two-sided blade, the most liquidity comes during tops & bottoms, so Steem misses out on a lot of natural high liquidity spots.
For security, we can have whitelisted withdrawal addresses, when changed, the funds are locked for a certain period. We can also find ways to add 2fa as EOSIO did here: http://bit.ly/38hdA9R
We can give users the option to remove the instant withdrawal feature if they don't want to use it. If they decide to add the instant withdrawal feature back, funds are locked for a period.
So burn to promote & a burn to instant powerdown are my ideas of ways to create bullish sinks for Steem.
Any suggestions? Comment below if you have any ideas for Steem sinks.