Not really, you’d just be decreasing the overall circulation of isk in the system. I’m not saying CCP should remove the isk sinks in the market, just add more in other places.
For example, hiring npcs to protect structures. They wouldn’t have bounties, or any loot worth killing them for, but it would create a fairly large isk sink when it’s all tallied together.
Another potential option would be an npc courier system. They could be attacked without concord intervention (just a suspect flag) so it wouldn’t be something people would use to move large amounts of valuables, but enough people would use it to move trash they’d normally keep stashed in random locations that it would end up being a decent isk sink.
The prior idea would also encourage more people to use region buy orders, thus more of an isk sink through the market as well.
A refurbished bounty system, complete with the ability to take out a contract on a specific person, which would give the player remote access to locator agents. There’s 3 isk sinks in that sentence. (Bounty list fee, contract accept fee, and remote locator agent fees everytime a request is made.)
Introducing “farms and fields” structures that could be destroyed without concord interference. Space farms for growing organics, manufacturing for w/e is grown at those locations, intel tools for exploration, ect. There’s several isk sinks in involved in all of that too. (Initial structure bpc / bpos, anchor fees, operation fees, and all of these items are potentially targets for those npc defenders too.)
Crew and Officers. If done in a lazy way, crew would just be an annoyance, but it could be a generally interesting addition to the game.
As you see, there’s several options I listed there, and it’s no where an exhaustive list.