As noted before, Anthony Beevors "Berlin" is a very good guide to how much of an issue Poland actually was both for the Allied and the Soviets. Whereas the Brittish supported the Polish government-in-exile and (especially Churchill) suspected Soviet motives when "liberating" Poland, the Americans simply wanted to apeace the Soviets to make the finishing of the war in Europe a quick affair to be able to re-direct focus to the Pacific. The Soviets during this stage arrested thousands of "counter-revolutionaries", many of which were Polish resistance fighters who often knew all too well the Soviets weren't going to give them freedom if so the war depended on it. It's quite safe to say Stalin had it in for the Poles, and the country suffered for it...
On a completely different note, I have actually had the Warsaw Uprising happen to me during a CORE game as the SU, and it was extremely annoying since the German garrison had just returned from the adjacent province after being beaten by my glorious Red Army, so, naturally, they were wiped out since they had 0 org... At this time, the Germans had little or no other troops in the area, which meant that the Poles could expand three provinces (west and southwestward) before I could encircle them... Now, since the Polish were in the Allies, I couldn't simply DOW them, and yet they were an extremely annoying obstacle in my advance, one that the Germans for some reason refused to deal with... (Though they might've been scared by the mighty Polish militia who annihalated about 16 german divisions after just one hours of struggle.

)
Anyway (this is getting way too long), I hope that it is included in HoI2 anyway, since it is (like in reality) a very real problem, especially as the Soviet commander, considering mostly the future of Poland, but also your invasion route.
[/Rambling]