As with many such miracle medicine queries, the answer is both YES and NO.
There are a couple things going on here that need to be addressed. First is the technical side of the question. From a merely technological perspective, the answer for most of these implant types is almost certainly a resounding YES. And many are a quite sure yes, even with present day technology.
The main problem your scientists (and our real world scientists) will have to face with some of these implants is getting the body to get with the programme.
Ocular implants: this is a no brainer in the YES column. We can already implant some pretty amazing things into the eye. If you place this implant within or upon the natural lens, perhaps using some kind of nanofibre attachments, then normal eye movements and focus adjustment will not be an issue, as the HUD will always be directed at the fovea (central vision).
The issue that will have to solved is how the brain interprets the data! As has been mentioned, the eyes are in constant motion. We don't notice it because we've had squillions of years of evolution and our brains are simply used to that motion and have adapted to "ignore" loads of extraneous data.
I am thinking that, perhaps, the problem could be solved by implanting the HUD, not inside the eye, but within the eyelid: the brain would properly interpret such a display as a (relatively) static visual input that is outside the eye and its constant motions. A person might acclimate to this kind of display better than in an intraocular one.
Aural implants: this is another no brainer on the YES side. Hearing is basically accomplished by sound waves that push a couple tiny bones in your head that cause some fluid to slosh around the movement of which tickles some fine hairs deep inside your ear. Those hairs tug on nerve cells that transmit the signal to the brain for interpretation.
But again, getting the body to accept the data is an issue that a mere implant may not be able to immediately solve.
We're bombarded by infra and ultra sound all the time, but we can't hear it, because that physical system is not set up to transmit those frequencies, and our brains aren't programmed to interpret the data. The implant is technologically feasible, but the brain is not compatible with the new hardware.
One could easily posit a workaround implant that "translates" infra or ultra sounds into audible frequencies. This would work exactly like an octaviser setting in a playback device. Basically, it translates deep tones into higher tones.
We already have implants that can boost hearing: this part of the implant will just be nanosized amplifiers.
Cerebral implants: this one I think will be the most difficult to achieve, and thus I think would be the least plausible, even for 300 years in the future. Unless we make great strides in understanding how the brain actually works, and what goes where within the brain, I don't think and implant will do what you want. It's not like we can just plug a memory card into the side of a person's head!
The main hurdle with any kind of external memory will be interfacing its circuitry with the highly individual circuitry of a person's brain. They will also have to solve various software compatibility issues between HumanOS ver.1.0 and the peripheral device.
Here, I'd posit that good old fashioned memory improving games and recall improving techniques will be more than adequate.
Bio-monitors: These are a resounding yes. There's no real reason why we can't make such a device even now. We already have devices that can continuously monitor blood pressure, temperature, blood gasses, respiration, ekg, eeg, and the like. The only hurdle to be overcome here is actually engineering an implantable device to accomplish these things.
As of 2020, we'd probably have to implant some wires to get a good ekg & eeg, but I'll give your future medical engineers the benefit of the doubt on that one!
As for disease gateway monitoring, I think that could be possible using a technology similar to that for the blood chemistry implant. Except in stead of looking for sodium and potassium ions, that part of the device will be looking for foreign chemicals: basically, an immune system analyser. I don't think this would be able to handle novel (or alien) diseases: as with the other blood analyser implants, you'd have to programme in the expected normal and abnormal parameters.
Muscle reinforcers: I think this would be a much more difficult and terribly invasive kind of implant. It's one thing to tuck an analyser somewhere in the abdominal cavity, but it's quite another to interweave foreign structures within a person's muscles.
A solid programme of weight training, cardio, and overall health & wellness will do more for muscle growth, strengthening & repair that any implant will do.
Nutrition implant: We can already create such an implant. We can feed a person through IV using specially formulated parental nutrition. As an adjunct to the other circulatory system implants that you have in place, this would be little different. We've had implantable fluid filled reservoirs for years now --- breast implants being a prime example!
Breast implants (the saline type) can be filled from an external source, and we've also long had medication reservoirs that are filled vie hypodermic needle. Your implant won't so much accept a "pod" as simply act as a direct fill reservoir.
But here again, there is the human factor that will need to be dealt with. Humans don't just need food because its nutritious, but they also need the physiological and social stimulus that comes with it. We need to chew, we need to swallow, we need to digest. We need the aromas & tastes in order to be satisfied. Ordinary people won't be able to survive on your TPN implant -- they'll just go crazy if they can't eat a pizza! The only people subjected to this kind of treatment are those whose digestive systems don't work.
As a strictly emergency nutrition, I think such an implant would be feasible. But there again, the external solution beats the internal: just carry some ymmy peanut butter & chocolate flavoured nutrition bars with you!
Conclusion: Out of six proposed implants, I think only one is truly viable as well as plausible (the diagnostic implant).
Of the remaining five, I think all but the brain implant will be technically plausile but humanly unlikely. Simply because the normal, external solutions to the problems to be solved are & will continue to be superior. Only one of the four, the auditory implant, I think would be not only useful but also the most compatible with the human host.
The cerebral implant is I think the least plausible of the six. I would argue, though, that if your future engineers can solve the outlined issues, then there is no reason why they couldn't simply make a pair of bionic eyes and a pair of bionic ears and simply replace the ordinary human organs entirely. Just hook polyfocal & multispectral audio~visual input devices directly to the optic & auditory nerves!
