Tau military tech does include bionics. As mentioned, they term them "Hard Wired" in all codex releases. The tech is not just for battle suits. Fire warrior shas'la ( the unit sargent or corpral) and Path finders may use Hard wired gear. Gear includes, Drone controler, Target Lock, Multi tracker.
In Imperial Amour second edition there is a section that introduces the Pathfinder testfiring the new infantry scaled Rail Rifle.
The test was overseen by a Aun im presuming to be from the Fire Cast. The test firing showed the hitting power of the Rail Rifle, The test gunner had a hardwired multi tracker and target lock to allow him to interface with his weapon. During the test a feedback surge from the gun caused severe brain damage to the gunner.
(rule represented by Gets Hot) The Aun was distressed by the results and loss of life but was resigned that it was a price to pay to arm the Greater Good.
The Weapon was sanctioned for field use.
In the current Codex release the Tau Rail Rifle no longer sufferes from feedback ( Gets Hot) and may use it and the hard wired gear in a unit of pathfinders ( up to 3 models) So this would indicate that the Tau are investing in their tech as well as their biological interfaces.
Would the Tau use Prosthetic limbs? Why not, its the Tau/Humane thing to do for all the wounded war vets of the warrior casts. It would be a engineering and a quality of life issue to develope functional limbs at first. Later stronger limbs would be made possible with military applications to allow wounded firewarrors to rejoin the fight with the experience and now reforged limbs to combat the many enemies of the empire. Tau are very familure with robotics and programming of articulated limbs and the have mastered the surgical skills to implant war gear that is largly sensory in nature wired directly to the nural path ways of their brains.
If your asking for this kind of stuff, you must have something in mind ( no pun intended)
Ill leave with this. Weapons of mass destruction. Only known use of a modern WMD is the PC game release Dawn of war 2 soul storm. The Tau have whats called Arco Cannon that destroys higher lifeforms at the cell level. All lower lifeforms such as plants, animals and insects are unaffected.
In game the cannon is used to reduce the garrison forces in a territory that is to be attacked.
If you want to see it check out on You Tube.
Other weapons, probably Fission and Fusion bombs. The do have Electo magnetic pulse weapons. Infact they have emp grenades. This would indicate that they have mastered the tech for a city or regional level of capability as it is much harder to control and build a device with a emp effect that fits in the palm of your hand.
Mass drivers. Large rail guns are possible with the principles and materials available to the empire. Local asteriods could be brought to a targeted world and then loaded into a large open barrel of a mass driver. Tau seem to have access to 2 types of force to employ mass acceleration. 1. Magnetic 2. Gravitity.
A asteriod size of a bus traveling at hypervelocity would wipe out any major city on earth. If the Tau want to play basket ball over a planet, they could dribble rocks down on the heads of their enemies. It would be ugly ( and dirt cheap). Have no doubt, if the Tau want to kill a world, they have the tools to do it.