Provide medic a unique way to revive more dynamically at the cost of their gadget slot.
Currently, medics can revive using bandages at a higher speed than other classes, which is good, but they still need to lay against their target for 3-5 seconds to revive, significantly slowing them down and making revives actually pretty risky.
The defibrillator would work in the opposite way, you can revive someone instantly, but then have a 5 second recharge timer before it can be used again.
This would provide a much more dynamic way for medic to perform a core class role without it getting spammed, additional balancing could also be in the form of HP amount when revived using it.
Alternate use could also include a mildly useless but funny melee weapon.
If you didn't have to put yourself in extreme danger and basically stop any kind of momentum to revive someone, I think you'd start seeing a lot more revives and therefore a lot more teamwork.
CLARIFICATION: This would be in addition to bandage reviving, not a replacement.