That's a real conundrum that needs to be solved and I think I know how it would be solved. Hopefully a better solution comes or it stays without any rewards, although then people will probably sell their SPS.
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I think I know how it would be solved
You're thinking they will start printing more SPS? That would be a major mistake.
Hopefully a better solution comes or it stays without any rewards, although then people will probably sell their SPS.
I wouldn't be so sure... Whales won't sell because they want the governance power. Players won't sell because it has a too much influence on Ranked rewards. Besides, delegation rewards will remain. If anyone has too much SPS and doesn't use it in the game, they can delegate it for an APR.
And that's only with the current options, and I didn't even mention vouchers, the airdrop, or Soulkeep again.