If Germany plus Austria unifies in 1848, what does it look like?
Depends on what it looks like.
That sounds like an unhelpful answer, but it isn't.
The why and how are desperately important here. Does the Austrian empire completely collapse, leaving basically the modern nation of Austria to join?
Does Prussia conquer all of Germany?
Is it a Frankfurt Parliament based union?
Is it the Hapsburgs taking over all of Germany?
Your biggest problem with ANY such union is that the Hapsburgs had no intention of getting rid of Hungary, and the rest of Germany had no intention of accepting Hungary.
Bits like Czechia were quite acceptable to both sides, viewing 'Bohemia' as largely German anyway (although the Czechs disagreed, obviously).
Slovenia might have been snuck in as part of a slightly greater Austria than the modern state.
Croatia and Northern Italy would be really, really difficult to swallow.
And Hungary impossible.
So....
Unless we have a PoD and believable plan for such a union, we can hardly discuss its future. Sorry.