Implants are planned as troop upgrades, upping their skills and attributes at the cost of money and other balancing measures. One idea on the table is that, after specific implants are installed, no further stat gain in that area possible. For example, no further gain in Speed after giving your troop robot legs.
I think the end to stat gain after implants is an excellent idea, to expand on this a little, here are a few idea's of mine
Implants could be researched repeatedly (allowing for cross tech-tree markers at various levels of implant) and each time you research, the implant bonus goes up and the cost for implanting also rises accordingly.
Upgrade your implants already installed into your troops, wasteful of resources but allows for development of bionic troops (maybe with a harsh resource cost but reduced medical time?) This could lead to different troop development approachs from the gamers side, whether to upgrade early at an expensive yet not very powerful benefit or wait until the implants are developed to get maximum cost/benefit
Implants give passive bonus/minus to armour values.
A guy running a long with metal legs,arms and torso isn't going to be bothered by a SMG, but a Laser Rifle would ruin his day....
Software implants. Improving weapon proficiencies at a cost to your mind stat(or at a cost to other weapon prof's?)
Compulsory implants....this stems from agonising every time I lose a trusted trooper
when a trooper dies on the battlefield, they could have a small chance to make it back to the base hospital with a debilitating wound - leg injury with speed reduced to 10, eye injury reducing weapon proficiencies by half for example.
There could be tight time limits to when you can save a soldier by using implants (bionics would have to be purchased for the trooper before the healing began in hospital)
Congrats for an awesome effort for getting the game this far
cheers,
Shak