I've been asking the same question for years. It's funny that I was just about to start a thread bragging about the amazing HDR capabilities of the 5DIII…
I did a furniture shoot yesterday. I didn't take my 1DX. Instead I took my friend's 5DIII because it has in-camera HDR which WORKS… Unfortunately, this only works with a tripod. Since the camera takes 3 images and then combines them into one. Also, there is a little bit of cropping on the final image, so u always have to frame wider...
I also wish for the day my camera can see what my eyes see. Even the most expensive cameras can't capture a perfect sunset or a backlit portrait without a lot of tweaking…
Magic Lantern has a hack for the 5D and I think 7D that enhances the DR but it makes the image noisy.
My suggestion? Dual or triple Sensors. One for highlights and one for Shadows.
IF one sensor could be calibrated to "see" only the top range of light and the other the bottom, it could work…
I attached one image of yesterday's shoot. Taken with available light only… This photo would be IMPOSSIBLE with my 1DX. I am very impressed with it and it looks great. Check out the white curtain. U can see the trees outside and not a washed out 100% white curtain. and the detail of the orchids against the backlit. Also, no noise or distortion.
So, to the OP, get a 5DIII and a tripod and it will change the way u see things…
Technical info: 5DIII, Canon 24-70 F2.8L II, ISO 320, 28mm, F8.0, 1/20
Happy Shooting.