The first thing to note is that for most of its history, the rule of Swiss expansion was "don't put the fence out too far", or in other words, don't take territory that's too far to hold. This limits Swiss expansion a decent amount if we hold that same belief.
If I had to pick areas, I'd agree with Falastur that the areas Switzerland had responsibility for in the HRE, tiny little statelets here and there really, are the best bet but don't offer much in terms of actual territory. Switzerland was very tightly allied with one of the Swabian/Southern German Cities Leagues, although I forget exactly which incarnation of that it was, and if the Emperor doesn't interfere in that as he did IOTL, the Swiss have the potential to gradually absorb some of those free cities as their own cantons. Again, though, I doubt it would be a huge amount of territory.
In the end, we come up to the fact that Switzerland evolved the way it is because of its harsh terrain, lack of centralized government, and general mercenary/neutral spirit in European affairs unless it directly affected them. To get a truly expansionist Switzerland that can hold bigger and further territories in its grip leads to a change of at least two, if not all three of those things.
Not much potential for expansion.