No no, I think he means simply adding back the CPU mining capability to Bitcoin Core.
But they didn't remove the mining capabilities from core, they just removed the command for it. The code still exists.
The issue though is the scales we're talking about. ASICs are not just a bit faster than CPUs, they're orders of magnitude faster. So I'm not sure if even all Bitcoin nodes ran a CPU miner in the background, it would help in any type of attack.
You are right, they won't. We are talking about millions or at best one or two billion hashes per second for CPUs compared to hundred tera hashes per second (that's 100 trillion). They can't compare and even if ASICs went down there won't be enough blocks mined to reach the difficulty adjustment.