If you do opt-out, increase loot bonus for higher number wars
As you well know, many are requesting an opt-out feature. I run a clan which wars only at 45 and 50. If you haven't been a leader in those larger wars, you do not understand how much more work it takes to be successful as compared to smaller wars. Lots of coordination, lots of communication and lots of teaching members how to be effective.
An opt-out feature would naturally lead to a lot of smaller wars and 50 v 50 might be a rare thing. To balance the system, if we were to have an opt-out system, the loot bonus should be increased for larger wars to provide consequences for clans which have players opting out.