Bidbots are still seen as immoral, this solution wouldn't be, so you might have more than 30% going in there.

There would be more than 30 indeed. At least at first.

I do think an idea like this should be implemented together with more incentives to ACTIVELY engage in content curation as a whale as well.

Let's say that there is 100 in the pool and there are 100 vests drawing from it. Say, 50 is passive locking up that 50 percent. Then, some large delegations go to 20 new application adding 20 new vest draws. Now there is 120 vests drawing from the 100 and instead of the passive getting 50% the active take ~65%. Active users target the applications to earn and power up and they will continually grow larger and draw on the pool. Introduce SMTs and oracles and they might only be earnable through active usage and decent behaviour meaning that it could be possible that the passive stake turns active again. What this does though is take the people who truly want to be passive out of visibility and influence over the content on the platform.