The dark elixir storage MUST go up another level at TH8. My storage has been full for weeks and I've absolutely no use for dark elixir at this point in the game. My King has reached max level and my lab is constantly occupied. I regularly donate dark troops and often use them to raid - this does not help!
Another solution (perhaps a better solution) would be to allow the King to upgrade beyond level 10.
The problem here is that:
a. If just the BK can go past 10, it'd be impossible to max TH8 since you wouldn't have the storage space for it.
b. Extra storage space would leave only one level for TH9s to upgrade. Can't do that, adding more storage space would mean increasing the curve for heroes as well.
c. TH8 isn't meant to have all of the amazing toys. It's not how the game is structured, goes against the idea of the game as a whole.
TH8's dark storage holds 80k - which is enough to upgrade the barb king to level 18. It would be nice if we could upgrade him to level 15 at least.
And my lab is following a schedule. I'm upgrading troops/ spells in order of most important to least important. I don't need to upgrade my dark troops yet.