What is Britain had not entered WWII

[ConjurerDragon]

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In 1938, Churchill wrote a memorandum to Lord Halifax (Britain's Foreign Secretary), urging closer co-operation with the Soviet Union, the US, and a possible united front of France, the UK, the Soviet Union, and, at the least, a benevolent neutrality with the US. For it's part, the Soviet Union informed France that it would go to war with France against Germany during the Sudetenland crisis, and that it would support a Czech request for League action if France did not honor her treaty obligations [quoted from FDR by Conrad Black].

The soviet offer came to nothing because the polish government rightfully mistrusted Stalin’s intentions and would not accept that soviet armies march over their country. I would see Stalins offer in the same light that the UK offered to send forces to help Finland in the Winterwar that had to cross Norway and Sweden and whose real purpose would have been to secure the iron in the area.

Don’t forget the Polish-Soviet war that happened after the end of WW1 either and the polish mistrust is understandable.

After Bohemia and Moravia were annexed in 1938, the Foreign Policy Committee of the British House of Commons called for conscription, an all-party coalition government of national unity, and an alliance with the Soviet Union [FDR]. These views were also held by Britain's principal Dominions (Canada and Australia).

Austria and the Sudetenland were annexed in 1938. Bohemia and Moravia turned into a protectorate in 1939
https://en.wikipedia.org/wiki/German...Czechoslovakia

In the spring of 1939, the Soviet foreign minister, Maxim Litvinov, called the British ambassador to Moscow and gave him a proposal for a tripartite defensive pact between the USSR, Britain, and France. According to the proposal, each would be obligated to go to war to support any of the others in case of attack and to defend Poland, Romania, and Greece if any of those countries were attacked. [FDR]

It appears to me that even before Poland was attacked, that Germany was perceived as the primary enemy by all involved, and that alliance overtures were made by each. (Now there would be a much more plausible what-if....a USSR/British/French alliance going to war with Germany)

Churchill did see the USSR in the same light as Germany. Not only did the western Allies of WW1 occupy parts of Russia to prevent their equipment falling in soviet hands but the USSR was just as much a Pariah in international politics as Germany was - which was a major reason that both cooperated between the wars.

Material aid was considered and actually planned for the Finns, but thankfully was never carried out as it would have been crushed either by the Soviets or the Germans, and would have gone a long ways towards pushing the USSR and Germany into an alliance (at least for the short term).

The plans to aid Finland came twice
https://en.wikipedia.org/wiki/Franco...the_Winter_War
https://en.wikipedia.org/wiki/Plan_R_4
and both had their problems.
The first problem is that the plan required neutral states like Sweden and Norway to let the armies of the western allies pass through. Both were not amused. Remember that military forces passing through neutral states is usually condemned by the same western allies (e.g. Belgium in WW1, Belgium, Netherlands, Luxemburg in WW2). At the very least that would have given Germany a valid casus belli as both would be aiding the Allies.
The second problem is that the whole plans true intention was to send some token aid to Finland but to occupy the northern part of Norway and Sweden to prevent the sale of iron from there to Germany.

Would have been a disaster for the very same reasons cited above. Bolsheviks and Nazis would certainly be an odd couple, but you can't box them both in and not expect them to co-operate with each other on some level

and odd couple? Churchill spoke out against communism almost in the same vein as Hitler, yet both cooperated with the USSR
https://en.wikipedia.org/wiki/Winsto...e_Soviet_Union
That is Realpolitik.

Given that Japan needed access to both China's and Korea's coal for making coke (steel-making folks...not the other kind), why would they agree to this? To say nothing of losing face to what Japan considered as a sub-human race...

Because Japan needed oil from imports more than coal from China. After all coal was already present in Korea and Manchuria (and even FDR’s embargo if understood correctly only ever asked them to get out of China proper, not Manchuria or Tsingtao).

After the debacle at Khalkin Gol in 1939, only the extreme IJA hardliners still favored war with the USSR. It had become painfully obvious that Japan's deficiencies in armor, artillery, and especially in unit mobility would make any venture against the USSR costly until those deficiencies could be rectified. (In fact, Japan's AGS felt that an initial breakthrough could be managed against the Soviets, but exploiting such a breakthrough would be extremely difficult due to Japan's lack of trucks and mechanization.) Personally, I don't believe they could even manage a breakthrough in any kind of terrain where Soviet tanks could operate

What would Japan stand to gain other then a very long casualty list? The oil, bauxite, and rubber in the DEI was much easier to acquire against a much weaker opponent. Siberia/Mongolia has lots of.......well, one has a lot of very dry badlands, the other a lot of snow and ice

First of all losing against the USSR at Khalkin Gol lead to some feelings for revenge in part of the japanese army. It showed them that Russia was no more the pushover it had been in the war of 1905 in which imperial Russia lost Sachalin and the protectorate of Manchuria and any naval credibilty to them. However from Japans point of view (as in being even more isolationist than the US have ever been and woken up by Perry’s naval forces to a world in which imperial powers turn anyone outside Europe into colonies) that means that the USSR had become the same obvious threat that Russia had been when it pushed it’s colonial border into China three times
https://upload.wikimedia.org/wikiped...0/Ct002999.jpg
Japan operated a while pretending not to pursue imperial ambitions but - just like the US in the Americas with their Monroe doctrine - as a liberator of native asians from colonial overlords. So war against the USSR would have been a justified war with a casus belli - after all Pu Yi was the emperor of Manchuria and the last heir of the Quing so a war to get the USSR to give back their stolen lands could at first look be justfiable for the view of the US so that they would stay neutral and deliver oil and further their agenda to be seen as the Liberator of Asians from european colonialism.

One other note; the German attack on the USSR came as a complete surprise to the Japanese as well as the Soviets. Japan's closest ally hasn't even bothered to inform her of Germany's plans to invade

Surprise - sure. Complete surprise? Everyone at the time who read "Mein Kampf" or listened to the speeches given about "Lebensraum" would have known that the Nazi party intends to go beyond just revoking the treaty of Versailles in the east sooner or later.