To reframe your question: WI Japan attacks its closest ally and major financial backer, entering a war with three Great Powers whose combined strength in the Pacific can overwhelm Tokyo. This entirely voluntary war of choice will force them to commit vast numbers of troops to the continent, especially given that this choice will absolutely bring the Beiyang government into the Entente since it's the easiest possible win for Chinese prestige. This war also gambles that Japan will not only achieve a total victory across the whole of East Asia- at a minimum seizing Outer Manchuria, Northern China, Indochina and large areas of Southern China and the Yantgze Basin - but also that Japan's allies in Europe also achieve so total a victory that Britain and France don't respond to a loss to the Central Powers by sending their European navies to Asia to crush Japan.
We're not even talking about the fact that by launching a surprise attack on Japan's ally, the Japanese have given substance to every deranged white supremacist fantasy of the naturally treacherous Asian, likely increasing American support for the Entente and definitely increasing Canadian and Australian commitment to the war, while also making it hard to achieve any negotiated peace.
Who on earth in the Japanese government is stupid enough to take that risk?
The best part of this is that it asks why the heck would Japan do this, because of the bad correlation of strategic forces and the isolated position Japan would be in, considering the good alliance they had, and the nontrivial, though modest, gains, they could make from their OTL course.
The flaw in the paragraph heaping all the disasters upon Japan that will ensure if they side with the CP is that it assumes that greatly superior Entente strategic capacity, even greatly superior, globally distributed forces, automatically and promptly translates into superior or adequately superior tactical or operational capability *where the Japanese would be operating in the near term*.
Going through some specific points:
This entirely voluntary war of choice will force them to commit vast numbers of troops to the continent, especially given that this choice will absolutely bring the Beiyang government into the Entente since it's the easiest possible win for Chinese prestige.
There is no absoluteness to this prediction
at all, even if it seems self-evidently strategically brilliant and obvious to you. Sure, China's Beijing government *could* declare war on Japan, to win the favor of a global alliance that has a larger population, more territory and looks stronger on paper, and could help it get revenge on Japan.
But was China in 1914 and 1915 up for the rigors of war with Japan and ready to be the primary recipient of Japan's military attention, just to boost its "prestige"? I don't think it had the illusion it was, or that it would be the "easiest possible win". If China was in shape to go to war with anyone, and looking for the "easiest possible win", Yuan Shikai's Beijing government would have certainly declared war on Germany after Britain did so and began its blockade, and started assaulting or besieging the German enclave at Qingdao. Instead, what China did was dilly-dally and wait, and let Japan declare war on Germany in September first, and start its siege, making it too late to act on its own. Then it later resorted to whining to try to get the concession land back.
Prediction: China's Beiyang government will stand aloof from this Japan and Germany versus Entente fight, and certainly at least wait to see which way the wind is blowing, before committing, and may never commit before matters are decided without China's input. Beiyang forces indeed may stand aside as pathetic witnesses to combat between Japanese and German (and tiny Austro-Hungarian) forces in Chinese ports and cities, fighting against British and French and Russians forces and legations in Chinese ports and cities.
While the British fleet supported by the Dominions is a superior force, and more so when augmented by the French, only so much of it is around Japan and in the China Seas, and the Entente fleets have multiple things to do in European waters, the Mediterranean, the Indian Ocean, and the world's other oceans. Additionally, there would be a certain augmentation and synergy of the German Far Eastern squadron and IJN being able to cooperate and use each other's facilities, especially against Russia's Pacific coast and in the China seas against French Indochina.
The Japanese betrayal will activate racial and racist fears certainly, but that by itself won't magically speed up America's effective war readiness or politically bring America into the war. I could imagine it harming US-Japanese trade. It would confront the US with a novel position it did no grapple with in OTL WWI, a belligerent state it disliked and heavily distrusted (more than the Irish-American community made it the case with Britain), that is physically capable of trading with the USA, and eager to buy US goods.
It is correct Canada and Australia would be alarmed. Probably to the detriment of both countries' contribution to the war effort against Germany. The Canadians will probably insist on an excessive number of ships on their west coast and an excessive garrison in British Columbia. The Australians and New Zealanders will be reluctant to deploy outside of the Pacific approaches to their homelands, which is bad for Britain's Middle East campaigns.
. In this case the 'closest alliance' rhymed into the the anglo-japanese alliance.