Not so much evidence (from trials, say), rather plausibility. We do not understand how Homeopathy works, but it goes even a level deeper: There is a certain and very specific process for creating those homeopathic remedies and from what we currently know about, say, physics, that process cannot leave you with some sort of active ingredient. If homeopathy were to work, our understanding of physics (which we have lots of evidence for) would most certainly be wrong in some ways.

That doesn’t mean that homeopathy is definitely wrong, but it does mean that the signal should be very strong for us to even be considering it to be not wrong. There are also levels to this: I’m pretty sure there are remedies about which we don’t know how they work, but them working would at least not require us to overhaul the laws of physics. That’s still worse than remedies for which we already have a model of how they work in mind, but at least it’s something.

Although you can’t really quantify that, I think such plausibility arguments are vitally important for any research. In fact, since time and money is limited, all researchers (in any field) will always try to limit themselves to what is plausible. Explaining why your model and your hypotheses are plausible is a big part of any scientific work. Plausibility is already a big part of science.