This does not really involve the direction of expansion proppsed by the OP, but still it is a distinct scenario by which the Habsburg Empire could swell really massive.
During the Revolution of 1848, Franz Joseph has a liberal-national change of heart, concedes a liberal constitution and federal autonomy to the various nationalities of the Empire, and accepts federal separation between Austria-Bohemia, Croatia, Lombardy-Venice-Trent, and Greater Hungary (including Galicia). Austria-Bohemia is recognized as a member kingdom of the German Confederation. As a result, the Frankfurt Parliament establishes the unitary federal German Empire under the GrossDeutchsland solution, and it offers the imperial crown to Franz Joseph, which accepts. The thorny issue of the rebellious Italian possessions are best dealt with by ceding them to Sardinia-Piedmont to create an effective buffer state in northern and central Italy (the various minor states of Central Italy soon join the new Italian state by grassroots revolution) in exchange for a treaty of alliance against France. As a result, the personal union between various domains of the Habsburg Empire stretches from Scleswig to Bozen and from the Rhine to Transylvania. Of course, the key issue here is whether Prussia accepts to enter this Empire, but the Prussian King of the time had all kinds of quirky romantic pseudo-medieval idea, he might just accept a liberal-national Empire if it lead by a progressist Habsburg, with the clout of historical legitimacy that dynasty carried from the old Empire, esp. if he is pressured by liberal nationalists within Prussia.
Schleswig-Holstein can be quickly won in war against Danemark. Russia can be won by ceding Galicia and promishing support against the Ottomans. France most likely tries to reverse the result by war in 1849, but is checked by the combined strength of the Empire and the alliance with North Italy. Britain can do little.
The result would be more or less like this, even if Italian lands and Galicia would have most likely to be ceded to make a sustainable geopolitical settlement.
Unfortunately, no OTL Habsburg scion was nowhere farsighted enough to see that by siding with the liberal-national movement in Germany and their own lands in 1848, a window was opened to make their Empire the top great power of Europe. It's not a terribly likely scenario, but it's not wholly unplausible, either.