merely preparing and testing is a form of pre-emption because it is enough to scare the hell out of miners so they do not attack in the first place.
Or they prepare counter-measures to whatever is (publicly) tested, because they are too belligerent to back down, tail between legs. I seriously doubt your scenario.
We already see Jihan opening up and looking for a compromise by the mere mention of a PoW change.
Or buying time.
I pretty sure you don't get it.
Bitmain et al don't care about their infrastructure, or negotiating, I'm convinced you've never dealt with sufficiently pathological characters to understand this.
Forget their words, or rhetorical actions, and look strictly at what their primary mode of behaviour adds up to. They will do or say anything in order to get what they want; the destruction of this currency and it's economy.
Decisive, strike-first and belligerent evasive action is probably the only thing that can save the value in the Bitcoin network as it is today, and if you can't see that, and some surprise move that nobody (except apparently me) anticipated sends things into even more of a tailspin, then you and everyone else who are saying "let's talk and pro-crastinate on our options for another 9 months" will get everything you deserve.
To put it another way, imagine that those directing Bitmain's actions have a planned killer blow to land. Do you think they're going to announce it 6 months in advance on a public forum? We must act, we're being forced into an "eat or be eaten" situation, and you can't see it.
Do you really believe that they can produce a Equihash, Keccak, or ETHhath asic in 6 months?
We should also be prepared with a secret backup HF algo tested and ready to go in the event they do indeed decide to attack with a secret ASIC, this should alleviate your concerns. If your concern is that they will fund gpu farms to attack , than we should be pushing for a Equihash and /or Ethhash merge mine option to protect ourselves.
There is something to be said with maintaining the moral high ground as well.... defensive only approach will attract many more people and thus much more investment , trust and security as we already see from the fact that almost everyone wants defensive only.