While the Amarr implantation of holders is meant to be both flashy and useful, medically it doesn't fundamentally differ from the Gallentean approach. An artificial liver or a heart is an artificial liver or a heart, no matter where it is installed. Some very old sources do indicate, though, that purely decorative implants were also a trend for younger Holders, since implantation is associated wit power in the Amarr society.
For the military, I'd most certainly assume that the most useful implants would be C3I (Commond, Communications, Control and Intelligence) related implants, interfaces to different equipment and sensors. A soldier that could hear like a dog and see in the dark, for example - with a built-in radio interface to report to the command post. Kind of an equivalent to what we see in space - near-total battlefield awareness by almost instinctive reports from soldiers. Some commando types might have strength modifications, such as enabling them to cross terrain at superior speed compared to regular soldiers.
And then, since people like things that make other things go boom, perhaps such things as integrated ocular implants to smart guns. In PF a quick draw implant has been mentioned, I believe. In addition, there might be other similar applications, such as automatic targeting implants. A sniper detects a target with his enhanced senses, assigns the implant suite a target which checks the integrated rangefinder on the cybereyes, calculated wind strength based on available cues and then starts to track the target. On command, the weapon is fired. Target down.
Or, back to my other example, a commander might be receiving coded messages from the front-line soldiers about a group of enemies detected. The commander lays his hand on a self-propelled gun and gives bombardment targets via implanted connection. Field gun executes orders, the other people die for their whatever.