You could add some lesser-known/more radical splinters:

Batenburgerites, based off the radical Anabaptist Jan van Batenburg, have a preference to the Netherlands & Northwestern Germany

Philippists, based off the reformer Philip Melanchthon, have a preference to Saxony, Brandenburg, & Central Germany

Davidists, based off the Anabaptist visionary Nicholas David, have a preference to Moravia & Silesia

Palatinate Calvinists, based off the localized Calvinist tradition of the Electoral Palatinate, have a preference to the Rhineland

Bucerians, based off the reformer Martin Bucer, have a preference to Alsace & Southwestern Germany

Pietists, based off the devotional renewal movement within Lutheranism, have a preference to Saxony, Brandenburg, & Scandinavia

Antinomians, based off the radical rejection of moral law within Protestantism, have a preference to England & Central Germany

Cromwellian Puritans, based off the Puritan faction tied to Oliver Cromwell, have a preference to England, Wales, & Ireland

Bodnics, based off the fictional Celtic-influenced Protestant movement in Cornwall and Brittany, have a preference to Cornwall, Brittany, & Wales

Patriot Reformed, based off nationalist-infused Reformed movements in occupied territories, have a preference to the Netherlands & Switzerland

Vossians, based off the theologian Gisbertus Voetius and his strict Reformed orthodoxy, have a preference to the Lowlands & Western Germany

Here are some hypothetical splinters:

Teutonic Reformed, based off a hypothetical Protestant order in former Teutonic lands, have a preference to Prussia & Livonia

Celtic Reformed, based off a Protestant revival blending Gaelic traditions with Reformed theology, have a preference to Ireland, Scotland, & Brittany

Danubian Brethren, based off a unifying Protestant movement along the Danube, have a preference to Austria, Hungary, & Serbia (More Austria-Hungary flavor?)

Steppe Reformists, based off a Protestant-aligned revival among nomadic steppe peoples, have a preference to Crimea, Ruthenia, & the Pontic Steppe

Hellenic Reformists, based off a Protestant revival within Greek Orthodoxy, have a preference to Greece & the Aegean Islands

Saharan Evangelicals, based off a Protestant missionary tradition among Saharan trade cities, have a preference to the Sahel & North Africa

Coptic Reformists, based off a Protestant-leaning movement within the Coptic Church, have a preference to Egypt & Nubia

Levantine Protestants, based off a reformation-aligned movement in the Levant, have a preference to Syria, Lebanon, & Palestine

Nestorians, based off hypothetical Protestant-aligned Assyrian Christians, have a preference to Assyria & Mesopotamia