““a number of challenging practical questions, including how the planes could actually be transferred from Poland to Ukraine.”
No European nation is stupid enough to fulfill this white house wet dream.
Other powers have their own interests which can drag other in even if they weren't planning on it.
My guess is that if the Ukrainians continue to resist, Putin will escalate until NATO or the US intervenes, because he can't make concessions to Ukraine, it's too humiliating. But he can make a deal with NATO or the US.