Worse Matchups / Longer Waits
So, to be clear, you are proposing that wait times for war pairings are longer and/or more unbalanced?
Think this through ...
1. Matchmaker would have to find 7 other comparable match-ups (instead of 1) for this to be fair.
2. If 50% of clans opted for this, that takes 50% out of the general pool ... doubling the time it takes to make matches as well as increasing the probability that the "best match" is unbalanced. (For example, if your "best match" is doing your tournament, you will get a less balanced opponent in regular war.)