You can't know what a research will bring, maybe it will be discovered that you can do all these tests through some proxy measurement etc. In biology they don't deal with "laws of nature" in the same sense with the physicist, therefore everything is engineering problem since you always have the option to go above or below the biological processes.
You can't transplant a heart until you find a way to do it, you can't change genes until you find a way to do it.
There's no natural law prohibiting measuring something something from the finger that can be measured from somewhere else, it simply cannot be done with the current methods due to some process going on in the human body. The task would be to find a way around the mechanism that is preventing you doing it.
"single finger prick drop of blood at levels that consistently correlate with venous levels" is definitely not one of the fundamental laws of nature. They may not correlate but maybe it's possible to acquire the information about the body through some other channels. It's not like there's a single way of surveying the body, right? A specific test can be impossible but another method can be develop for obtaining the same information.
Blood test nerds can be disappointed, of course. I doubt that the core audience are the blood test aficionado, but you can always make them happy by saying "We are confident that the test can be done through single drop of blood in 2 years".
If a doctor needs the patient's current platelet count for treatment they're not going to be able to get it through a nasal swab or urine test or whatever. This is restrained by fundamental physical laws. If you're still not getting it then all I can suggest is taking a remedial biology course.