How Pilsudski was generous to Serbians? How? Man, Serbians were military elite of Polish-Lithuanian Commonwealth. Those were Serbs who gave Winged cavalry military `knee to knee` doctrine to Poles, what was cutting edge in military war-craft. Not only that. Serbian ways were welcomed by Polish Jagilonian kings and whole of Polish nobility. Serbian gusle music players performed at the court of Władysław II Jagiełło since 1415. Serbians, as Racowie, entered in Polish epic legends.
So logically, Pilusdiski couldn`t imagine new Commonwealth without Serbians.
As for Czechs and Slovaks, I don`t know what went wrong between Poles and them. Strange. But, in any case, when it comes to Intermarium they will follow Serbs. So again, Pilsudski needed Serbs. Russians? Well, again Pilsudski needed Serbs. Only Serbs were reliable factor when it cames to Polish-Russian conflicts. For one, Serbians for their own interests acted as perfect mediators between Poles and Russians. Then, if Russians acted against Poles, Serbians ignored Christian Orthodox religious factor and sided with Poles. Unique example of ignoring such a factor, not only among Slavs but among all Europeans. See, Serbians are first Slavs (ie Sarmatians)- in ethnic and spiritual sense and, just then Christians. That fascinated Pilsudski. And not only him but also Adam Mickiewicz, prince Czartorisky and others.
For Croats, you are right. But, its not over yet. While Croats for sure have their right to go with Germany, Catholic Serbs would be saved from Croatian yoke and free to join with other Serbs and that way keep themselves and their property within Slavic (ie Sarmatian) realm.
Baltics, Finnes? Well, how things stands now, forget them. We have to be realistic.
Who knows what Serbians would have done if they were accepted into EU, after what Croatians have shown so far, I am sceptical about any Yugoslavians.
If you are familiar with Polish history, you wouldn`t have any doubts about Serbs.
Ukraine? Yes, dialogue, after Ukrainians make a deal with Russians about borders between of what would be Ukraine and Russia.
Belarus, Romania? Dialogue is good thing. Always.
Bulgarians? Well, same as Croats in history proved how Catholics can serve to Germany, Bulgarians proved how Orthodox can serve to Germany. Now, go figure that.