As is there were uprisings in Poznan shortly after Khrushchev's "Secret Speech." I would think this admission within it would massively add to that, making a Polish Crisis even larger than the Hungarian Crisis later that year.
IOTL, tensions eased once Gomulka came into power and yielded some minor reforms. In this case I would expect much more would be needed to pacify the people. Eased restrictions on the Roman Catholic church perhaps... Or else, the Soviets double down and destroy the insurrection by massive force, therefore looking hypocritical in censuring Stalin but maintaining his hardline approach and giving loads and loads more political capital for the West to use against them.
And of course, as the Hungarian Uprising was IOTL part due to a need to see similar reforms as Gomulka gave to the Poles, it is not a stretch to see the butterflies influence this as a result. Either Nagy has to give up far more, or possibly there is a massive period of rebellion within the Warsaw Pact.
Either way, DeStalinization just got a bit trickier, at least in 1956... Reasonably likely it is all under control by '58 though.