Crystal Tower is becoming open to Free Companies soon, isn't it?
24-man races, begin!
BCoB is unlocking in patch 2.2 so players can run 1-5 without being locked out.

I feel there is no issue with the sizes of dungeons and players being able to queue for content.
Yes, the perfect size currently is 8. If you have 7 really good and consistent friends, you'll be laughing and destroying content all over the place.

If you have 7 unreliable friends, being in a FC with 100 people means you have substitutes, people on different stages of progression willing to help you on on your second relic, and other dungeons.
However, more 24+man content would be incredible...