First of all - Pilsudski died 1935, 4 years before the nazi invasion of Poland.

While on paper Prometheism might look dangerous to the Soviets, in reality, Lenin and later Stalin had little problems with nationalist insurgencies once they had won the Russian civil war. The Soviet state was strong enough to carry out brutal mass murders, go through famines and forcibly resettling large ethnic groups without wide-scale insurgencies.

Poland was not strong enough economically ormilitarily to champion nationlistic rights of Ukranians, Byrelorussians, Kazaks, Chechnyans and the many other ethnic groups in the Soviet Union.

Poland viewed the Soviet Union as their primary and most dangerous enemy until 1938 or so - with good reasons. Before the expansion of the Heer, the absorbation of Austria and the dismemberment of Czechoslovakia, Germany was militarily weak and surrounded by hostile nations and faced a two-front war - France and Britain on one side and Poland on the other. The French army was widely regarded as the strongest in the world at the time.

The Soviet Union did not look like it was weakened by any Polish efforts post the Polish-Soviet war in 1921 - rather they finished their civil war, launched into a campaign of heavy industrialisation and built a huge army with enormous amounts of equipment, becoming more of a threat to Poland than they had been 1919 or 1920. If Pilduski's plan was working, I doubt this would happen.