I suspect that vanilla furnaces wouldn't be able to do this unless they were replaced/coremodded but I thought I'd see if it's even possible to do this.

Feature request name
furnace recipe output weight support

Feature request description
Support for output weights like crafting table recipes have. eg. 50% chance of distilling a speed I potion to a glass bottle and 50% to speed II potion

Feature request reason
A vanilla-ish way to distill containers with liquids like potions or alcoholic drinks?

Feature request dependencies
Ideally wouldn't need other mods

The Vanilla Furnace is a 1:1 Map, there is no way of having it chance based without rewriting the whole furnace registry or replacing the furnace with something else.

I suggest you look for a mod that allows what you want to do.
If you want to "distill" items in a vanilla-style way, why not use the Brewing stand?

As kindlich said, not possible.