Hungarian seccession in Vojvodina and the IStrianism in Croatia are nothing but pure kiddo tendentions from Stormfront and similar forums. Most Magyars fled Vojvodina in the last few years just because Hungary gave them their passports and they went to live in Western Europe. There are almost no children in the Magyar-populated parts of Vojvodina, and in general, Hungarians are calm and concentrated to their personal and family well-being rather than nation-related affairs.
Similar is with Istria. The Istriani movement is more a political response to nationalism and centralization that are strong in Croatia. IStrians are known as devout leftists and "commies" and the area is ethnically very mixed, but has no bright future as a standalone country. Dalmatians have a more seccessionist stance than Istrians do, as they can't really stand people from Zagreb and central Croatia. So maybe one day they make an independent "Croat Republic" consisting of Dalmatia and Croat-populated parts of BiH. The remainder will be Croatia as we know today and will contain Istria.