Apple's iPhone 7 Plus decided to add another lense to be able to make better pictures. Meanwhile Walabot who started with wanting to build a breast cancer detection technology released a 600$ device that can look 10cm into walls. Thermal imaging also got cheaper.
I think it would be possible to build a 1500$ device that could combine those technologies and also add a laser that can shift color. A device like this could bring medicine forward a lot.
A lot of area's besides medicine could likely also profit from a relatively cheap 3D scanner that can look inside objects.
Developing it would require Musk-level capital investments but I think it would advance medicine a lot if a company would both provide the hardware and develop software to make the best job possible at body scanning.
That's the wrong analogy; we're talking separately selling a device that tells you some metric, not a diagnosis like breast cancer. So presumably you have to compare it against some existing way to measure that metric.
I don't know how much testing & FDA approval normally costs for nontrivial "metric only" devices (e.g. glucometers), but on the outside view, I doubt it's cheap as you say, because everyone in the system has incentives to raise the price, just like for drug trials.
And product wise that would result in the same kinds of products we have now, i.e. extremely conservative and slow moving. And approved and marketed for just a few uses, instead of being open-ended like you suggested.