The context would settle the dispute :)
All in all, "only in Poland" should be construed accordingly. If there's such a possibility of using "it" in an appropriate context, shouldn't we shorten that headline ? It's the same with headlines in news, they are more like separate words fused together to form " a good syntax".
If this is the case "Only in Poland = unique" can be used to form such a structure, so I would stick to mine, if I had more context to fit into.