There are a few big misconceptions floating arouns here:
1) European powers were "expansionist" as a blanket statement, especially within Europe. Bismarck was against taking A-L. Austria couldn't afford to expand. Britain never set foot in Europe. France and Russia were generally conservative in their aims. I see no reason why a liberal state would gallavant off in search of Lebernsraum.
2) Russia was pan-Slavist in the 1840s. Pan-Slavism arose in the 1860s. It subsequently
failed, with its tiny artificially-shaped offspring Bulgaria spending much of its early existance resisting Russian influence. In 1914, backing Serbia was a matter of strategy concerning the Straits, Balkans, and Middle East dressed up in Slavic solidarity.Slavic brothers my arse: look at the Polish-Russian brotherly-love fest that took place in 1867. That just goes to show that Orthodoxy was a big part of Pan-Slavism and Russia (which is to say, teh one faction in Russia that is pan-Slavist) doesn't really give a crap about Slovaks.
3) Britain was not isolationist in the 19th Century, we just tended to see binding agreements as restricting and unnecessary because of our supreme security, but we were pretty proactive on many European issues.
As for the question, what will happen if the Frankfurt revolutionaries have for the sake of argument taking over Austria is that being liberal German nationalists they will immediately grants Hungary, Galicia, and Croatia independence. There is no way they could be inspired to keep thousands of nationally self-aware non-Germans with their own liberal revolutionary movements inside their liberal empire.
I have to question whether everyone would dogpile them as quick as people are suggesting. Their physical power is no greater than that of the pretty well permenant Austro-German alliance of later in the century, and this is at a time when Germany is much
less of an industrial collosus. Russia, however, would be alarmed not only by the new German blocs physical power but also by it being a child of The Revolution
eek:!!), nut revolutionary France and Italy and liberal Britain seem less likely to jump in to me.