This may very well be a pathway for some believers of ID, but it won't do for me. First, I don't accept negative assertions as a scientific premise. By that I mean ID surmises that in the absence of another explanation, it wins by default. I don't buy that.
Instead, it needs to support its assertions by showing actual evidence of an intelligent designer, and not merely the lack of evidence saying there isn't one.
Second, I don't see how complexity beyond our current understanding can be quantified as gradients of extremity. Either we understand it, in which case we can judge its complexity, or we can't, in which case we simply know it is currently beyond us. But by continuing to study such an object, we can begin to realize its intricacies a little at a time. Eventually, we might know enough to start making predictions about its function, or maybe discover that there is even more to it than we first imagined and be even further away from figuring it out than when we started. In either case, as we keep studying and learning, it inevitably will become understood by man. Or not, but that shouldn't keep us from trying.
I guess what I am trying to say is there is no level of extreme complexity at which I am willing to abandon the scientific attempt to master its knowledge. What is beyond our reasonable explanation today, as long as we strive to increase our understanding, will be common knowledge tomorrow.
I'm sorry, I cannot follow exactly what "limitation" you want ID to abolish
For ID to be considered scientific, it must abolish the limitation of science to the natural world, and increase its scope to include the supernatural.