There is no way to tell from a block if it was mined with AsicBoost or not. So you don’t know what percentage of the hashrate uses AsicBoost at any point in time. How can you risk forking that percentage out? Note that this would be a GUARANTEED chain fork. Meaning that after you change the block mining algorithm some percentage of hardware will no longer be able to produce valid blocks. That hardware cannot “switch over” to the majority chain even if it wanted to. Hence you are guaranteed to have two co-existing bitcoin blockchains afterwards.

Again: this is unlike the hypothetical persistence of two chains after a hardfork that is only contentious but doesn’t change the mining algorithm, the kind of hardfork you are proposing would guarantee the persistence of two chains.

That hardware cannot “switch over” to the majority chain even if it wanted to.