The named (human) elite defenders always drop a kit, the droids do not.
In the 14 solo-scenarios I farmed tonight, I saw a named defender 3 times and got a kit from all 3. So I'd guess the drop rate is somewhere around 20%, as it is with similar currency drops.
It would be interesting to know if groups have a higher chance of getting a named defender. If not, since you'd have a 1-in-4 chance of getting each one, your actual acquisition rate could be as low as 5%. But since they are relatively easy to farm for geared 78s, I'd guess they will be readily available on the GTN for 30-40k each in short order.
Yep got that, 1 per scenario but not 1 named per scenario ... named are rare spawn.
Groups are screwed at least at low level, 5% is good approximation.
It would go as Tauntaun data and BHW contracts - some will grind to sell, some will buy... hype will fall and market will stabilize.