Firstly I would like to congratulate you on coming up with this idea.
I do strongly agree with this, how when you search for a clan, it is extremely hard to find some of these clans. I know for a fact how hard it is with my clan, sometimes we dont even pop up, that is how hard it gets!
But i also disagree with this idea, that it throws away the right of having a clan, inactive or active, a clan is clan that someone put effort too, what if they all came back and found out what supercell did to there clan, I know I would be heart broken.
What if you had an clan where all your holiday makers go while they are away, or just need a break. Take consecration for example (
www.consecrationclan.weebly.com), they have there main clan and then consecration I.A where there inactives go. What happens to that?
Time could be discussed, but as stated before every player has the right of having a clan. Maybe if supercell some how monitor the active clans and stick them up the top and work there way down adding a 'load more' at the bottom.
To follow you up on the feeder clan issue, we have a feeder which is as active as our main clan, and has the same amount of members, a feeder isnt a clan where you can do whatever you wanted generally, it is a recruiting clan, where members can be transferred to the main if ever needed.
Finally, good luck on this topic, and I can't wait to see the end result :-)