Firstly, let me preface this by saying: This is a complicated subject with complicated implications. However, that doesn't mean it's unreasonable to conceptualize.
My first idea would be a neural proxy of some sort. Mind uploading, if you will. We'll need to increase the speed at which this uploading happens to a maximum of about 20 seconds. Any more could lead to loss of life.
Secondly, we need nerve interfaces. This is much easier, as you're just reading and coding nerve input. Now, it's going to be painful during connection, but said pain should subside after just a second or two. Easiest way to prevent this is by adding a proxy to the nerves, with a more permanent connector. It'll still sting, just not nearly as much.
Next we're going to want something other than just replaced limbs. I'm talking things like mounted holodisplays, internet proxies streaming directly to a neural interface, something like the Nexus that the Avali have. It's all absolutely possible.
Next we'll want flesh replacement. Bio printing has come a long way, and it just needs a little further, and then we'll be home free. We just need some rapid genomic analysis.
Then we'll need to work on armor. Something strong, like carbon with a titanium diboride ceramic shell, with neurohaptic feedback. Fell what you're touching, that sort of a thing.
Once that's done, we can work on creating species. That's where the fun begins. But that also brings me to humane testing practices.
Test subjects need to be treated like actual living beings. We don't live in the stone age. We know what compassion is. They also need to have routine maintenance as though they were being serviced like one would if they were out in the world. After all, you can't test something without an accurate baseline control group.
