If we combine the benefits of a human physiology maintained at the level of effectiveness possessed by our bodies when we were children (e.g., dechronification), along with the ability to deal with almost any form of severe trauma (via nanosurgery), then there are very few diseases or conditions that cannot be cured using nanomedicine. The only major class of incurable illness which nanorobots can’t handle is the case of brain damage in which portions of your brain have been physically destroyed. This condition might not be reversible if unique information has been irrevocably lost (say, because you neglected to make a backup copy of this information). There are several other minor “incurable” conditions, but all of these similarly relate to the loss of unique information.
Nanorobots constructed of diamondoid materials cannot be destroyed by our immune system. They can be made to be essentially impervious to chemical attack. However, the body may react to their presence in a way that may interfere with their function. This raises the issue of nanorobot biocompatibility.
The key issue for enabling full-immersion reality is obtaining the necessary bandwidth inside the body, which should be available using the in vivo fiber network I first proposed in Nanomedicine, Vol. I (1999). Such a network can handle 1018 bits/sec of data traffic, capacious enough for real-time brain-state monitoring. The fiber network has a 30 cm3 volume and generates 4-6 watts waste heat, both small enough for safe installation in a 1400 cm3 25-watt human brain. Signals travel at most a few meters at nearly the speed of light, so transit time from signal origination at neuron sites inside the brain to the external computer system mediating the upload are ~0.00001 millisec which is considerably less than the minimum ~5 millisec neuron discharge cycle time. Neuron-monitoring chemical sensors located on average ~2 microns apart can capture relevant chemical events occurring within a ~5 millisec time window, since this is the approximate diffusion time for, say, a small neuropeptide across a 2-micron distance. Thus human brain state monitoring can probably be “instantaneous,” at least on the timescale of human neural response, in the sense of “nothing of significance was missed.
It will probably not be possible to eradicate all infectious disease. The current bacterial population of Earth may be ~1031 organisms and so the chances are good that most of them are going to survive in some host reservoir, somewhere on the planet, for as long as life exists here, despite our best efforts to eradicate them. However, it should be possible to eliminate all harmful effects, and all harmful natural disease organisms, from the human body, allowing us to lead lives that are free of pathogen-mediated illness (at least most of the time). A simple antimicrobial nanorobot like the microbivore should be able to eliminate even the most severe bloodborne infections in treatment times on the order of an hour; more sophisticated devices could be used to tackle more difficult infection scenarios.
Regarding microbial adaptability, it makes no difference if a bacterium has acquired multiple drug resistance to antibiotics or to any other traditional treatment – the microbivore will eat it anyway, achieving complete clearance of even the most severe septicemic infections in minutes to hours, as compared to weeks or even months for antibiotic-assisted natural phagocytic defenses, without increasing the risk of sepsis or septic shock. Hence microbivores, each 2-3 microns in size, appear to be up to ~1000 times faster-acting than either unaided natural or antibiotic-assisted biological phagocytic defenses, and can extend the doctor’s reach to the entire range of potential bacterial threats, including locally dense infections.