How will this kill clan wars? Now, more than ever, effort put into the game to practice will have a significant impact on the outcome of a war.
Additionally, mismatches will has far less effects, now that weaker-matched bases can get extra practice on their stronger counterparts.
I'm speaking from personal experience for this, but I have put in a huge amount of effort into clash, watching videos, practising in war (The number of 0 and 1 stars in the beginning

) and slowly tweaking and experimenting. And some of which I would like to think is my own ingenuity! I've gone from a rushed th9 gowiper to a max th10 with 2 baby 9s. I 3 star regularly with my 10 and my 9s 3 star maxed 9s on a regular basis. I've always believed the skill truly trumps everything else.
But I digress. This isn't about me. Most of my clan aren't as hardworking or willing to put in as much effort as me. They are content with doing the occasional 3 star attempt with no modifications or adjustments from the last time they failed! That's terrible! With the introduction of this new feature, I'm hoping that it will give them more incentive to tweak their strategies to better achieve 3 stars in the future (They definitely have the troops for it, they just lack the experience that I've had).