You specified, specifically, a change in technology. So, my answer would be the re-introduction of eye-tracking autofocus.
This would be far, far better than the old eye-tracking AF systems. This would allow you to look at something thru the viewfinder, then "tell the camera" that this is the object you want to focus on. The camera would "remember" the object using technology much like face recognition. Then, whenever that object was in the frame, the camera would focus precisely on that object.
So, if I "told" the camera to recognize a butterfly, the camera would focus exactly on the butterfly, no matter how quickly it was fluttering around, and no matter how far away it got - even if it was a tiny speck in the frame, that is what the camera would focus on.
Better yet, I would tell the camera to focus on the butterfly's eyeball - then, when the butterfly was close enough to occupy a good portion of the frame, the camera would not just pick any part of the butterfly - it would focus precisely on the eyeball, just like I told it to. Yes, even if the butterfly was blitzing erratically all around the frame. As long as I can keep it in the viewfinder, the camera will focus on it.
This would completely eliminate the need to focus & recompose.
It would be especially helpful when I use long focal lengths - at 900mm the depth of field is incredibly shallow, regardless of what aperture I'm using. Sometimes, if I accidentally focus on a bird's beak instead of on its eye, I miss the focus and the shot is trash. Being off by just a centimeter is the difference between an awesome shot and a wasted opportunity. Frankly, my motor skills are often just not good enough to keep the little red box on exactly what I want it to be on, especially with a quickly moving subject.
This new generation eye-detect AF would mean many, many more keepers! Of course, it would be completely over-rideable, if the user chose to use a different focus mode.
There are many other changes I would love to see happen - but you said only one, and I think this would help more than anything else.
"Your" and "you're" are different words with completely different meanings - please use the correct one.
"They're", "their", and "there" are different words with completely different meanings - please use the correct one.
"Fare" and "fair" are different words with completely different meanings - please use the correct one. The proper expression is "moot point", NOT "mute point".