> Browsers have been trying this for a long time but its not simple.

I didn't say it was gonna be easy. I said it was necessary. This is a perpetual arms race. If content blockers can maintain their huge blocklists, browsers should also be able to maintain their own counter-measures to abusive websites. Browser vendors created and standardized the APIs that websites are now exploiting. I expect them to clean it up.

> then websites just check how fast the local data store is to check if it is on disk or in memory.

Making both calls equally slow should prevent this particular side channel attack.