How to set transparent property per object for fade in/out, without having redundancy of materials? Before you comment:
I don't want to have 200 materials of the same metal just for fading out at different times.
Render layers are out of the question too of course.

I bolded it out because I found here several quite similar questions and almost everytime someone who doesn't understand the problem of redundancy in complex projects advise to have the same amount of materials as fading in/out objects in scene.



I am working on couple of animations where lot's of objects are needed to be fade in and out at different times. 

Since the projects are quite complex to manage for me (and I already have plenty materials) it is not effective to, for example, have 200 different materials of the same metal just for fading them in/out at different keyframes.

Is there any way to do it using maybe Custom Propterties in object panel? 

I've tried using drivers on Custom Properties, but it always fading out all object sharing the same material.
You can use the object viewport color to force variation per-object, even if they share the same material.

The setup is quite simple :



If you are using Eevee, don't forget to tweak the blend mode and uncheck "Show Backface"



Add some keyframes and play :



Further reading on viewport color