Scenario A. We have some valued members that have been with our clan for a very long time, but they don't do clan wars. This is hurting us, but we really don't want to kick these members.
Scenario B. Occasionally a member is unable to play for a time and will be inactive in the next clan war. Again this hurts us in the clan war, but we don't want to kick this member.
Solution: Allow Leader and Co-Leaders to set certain members as spectators for clan wars. This option could be added to the menu that allows Leaders to kick, promote, etc. Add an option for "Spectator".
How this might change the game:
As you think through this option, you must consider all the ways that people might use this option and how that affects the feel of the game. You may find clans that only allow a select few to go to war while the rest spectate. I don't have a problem with that. If you want to find another clan that allows everyone to go to war, that works.
Leaders might use this option as a disciplinary action to those that disobey rules (i.e. low donations). Again, I don't see a problem with that. If it gets out of hand, people will find another clan.
As leaders catch on to using this feature well, clan wars will be less about "which clan has the most active players" and more about good defensive bases, individual attacking strategies and picking the best targets. Overall, I really like the changes this feature can bring to the game.