What do you think could (plausibly) cause this? A quantum attack on the ecosystem?

I think a systemwide security breach is unlikely, especially with Cardano's decentralised stake-pool setup (see Saturation Parameter - K).

https://cardano.org/stake-pool-operation/

The only other plausible "catastrophic" attack would be a quantum one, though I think this is unlikely by 2025. Moreover, according to Charles Hoskinson, Cardano is beginning work to become quantum-resistant for future anticipated attacks.

https://dailyhodl.com/2021/12/09/cardano-begins-work-on-becoming-resistant-to-quantum-attacks-according-to-creator-charles-hoskinson/

Then again, unexpected things happen in this space, so prepare for anything.

Thanks for sharing your insights.