Has Poland experienced "Fusion Cuisine" as yet?
Many centuries ago, and several times since.
Poland lies within several culinary continua on the Continent.
The first is the North Sea/Baltic continuum, spread primarily by the Hanseatic League in the late middle ages, and latter by the Prussians and Swedes. Foods like herring, smoked eel and salmon, red beets, kisiel, chłodnik, and staple foods like rye, barley, oats, buckwheat and, later, potatoes (originally from the Americas), are all typical of this zone.
The second is the Central Germany continuum, which reaches from Alsace and Loraine to Poland. Cabbage, sauerkraut and beans, both green and dried (also originally from the Americas) were big staples.
The third is the Southern German/Austrian continuum, and its sister branch in Hungary, which was highly influenced by Turkish cuisine. Schabowy, makowiec, sernik, gulasz, knedle, the many types of kluski and the przysmak Jon mentioned are all imports from this region, when Poland was under Austrio-Hungarian rule.
The fourth is steppe/central Asian cuisine. Pierogi and gołąbki are probably originally from there, though both have completely "gone native".
Some dishes were borrowed from Russia, especially the ubiquitous sałatka jarzynowa, which was originally developed by a Belgian chef in Moscow.
A lot of Polish cuisine died out during WWII, and food shortages afterwards under Communist rule did not help. But some new "fusion" dishes were promoted by the Communist government, especially Fasole po bretońsku and ryba po grecku.
There were also some French and Italian influences on Polish cuisine, too, going back to the late fourteenth century when many French and Italian monks moved to Poland after the Black Death. A lot of the vegetables that are attributed to Bona Sforza were actually introduced by monks, as were carp.
After the fall of Communism, Poles have started to experiment with various cuisines, especially Italian and "Chinese" (usually cooked by Vietnamese immigrants, and highly toned down and adapted for Polish tastes). They are not quite at the modern Fusion stage you are thinking of, though I'm sure you will find some adventurous chefs in the big cities that are experimenting with new ingredients, techniques and combinations. Younger Poles, especially those who have spent some time abroad, are much more adventurous than their elders who grew up during Communism and were accustomed to extremely bland food.