One criticism that is often applied to intelligent design is that it is fundamentally untestable and hence can never be scientific. But is this really true?
The classical notion of God is definitely untestable. A being that is intelligent and omnipotent, and doesn't want to be found for its own reasons, can do whatever it wants to avoid being found. It can hide indefinitely, and it can even plant false evidence to trick people into reaching the wrong conclusion about the origin of the universe. That's kind of what true believers are required to believe, in order to explain away the overwhelming lack of evidence for God.
There is an assumption among ID promoters that they don't need to come up with ways to test the properties of the designer; all they have to do is detect objects that have the property of being designed, and the nature of the designer can remain comfortably outside the domain of scientific inquiry. However, that's not necessarily true unless you assume that the designer is godlike -- which of course they do, even though they lie and say that they don't.
But I don't think that this property of being hidden from investigation should be true of all supernatural events in principle. What does it mean to be supernatural? I think the usual understanding is that it's something that exists outside the realm of the natural universe. But does this mean that a supernatural thing can do absolutely anything with no limits? Not necessarily. If the supernatural thing lives in its own universe, or its own metaverse, then that universe is probably subject to its own rules and limitations. Those rules wouldn't necessarily be the rules of our universe, but they'd be rules nonetheless, and would require anything in that universe to behave in a way that is, at least in principle, also predictable.
Is it possible to test what the rules are? Well, it depends. Really, the interesting question at work is whether the other universe can interact with this one. If it can, then it ought to be testable in some way. If it can't, then there is really no reason to care about it.
In the 90's there was this sci-fi show called "Sliders" about a small group of people who figured out how to "slide" into parallel universes. These universes had parallel versions of all the main characters (except in universes where the characters died or were prevented from being born), and they had separate histories. In one world, the British won the war of independence, and America remained a colony owned by a preserved monarchy. In another world, the patriarchal society was reversed, women ran the world, and men were considered weaker and often objectified as sex objects.
These universes had apparently always existed, but until sliding was discovered, they were completely irrelevant to this one. If you asked me right now, "Is there a universe where Kazim is the popular and successful pastor of a megachurch?" I would say "There could be, but who cares?" For the time being at least, "sliding" is total fantasy. If Pastor Kazim can never meet Atheist Kazim, and vice versa, then we have no effect on each other's lives, even potentially. I don't rule out the possibility entirely. I can imagine it easily. The problem is, there are so many different implausible things for me to imagine, that there's very little point in treating any of them as true without evidence.
If we ever proved that a supernatural entity did exist, it would only be because that entity interacted with the natural universe in some detectable way. Either a physical manifestation of something appears and does something, or we develop technology that can peer into the supernatural realm and see it there. Either way, there is an exchange of information between the two. And if that exists, then suddenly the supernatural thing is detectable by natural means. By some definitions, that would mean that the supernatural thing has become "natural." That's why I'm wary of calling things "supernatural": the definition is vague and kind of fragile.
But if we're slightly less ambitious in our assumptions about the designer's identity, there's no good reason to assume that we couldn't learn about it through experiment. It presumably stuck its finger into our universe at certain points in history, and altered the universe in detectable ways. (Remember, if it didn't do this then it's irrelevant -- just like Pastor Kazim may exist but is currently irrelevant to me.) If it did something we can detect, then we can see what the changes were and come up with likely mechanisms for how it interacts with our universe.
The only reason ID has to remain non-science is because they've set up a boatload of assumptions that make it non-science. As soon as they get creative and come up with hypotheses that can be confirmed or disconfirmed in some way, then they could figure out a way to do some legitimate research.
Just don't hold your breath waiting for that.