Every time Clash of Clans posts to Twitter or Facebook, someone in the comments asks for a gem mine. We never thought this would ever happen, but we now have one in the Builder Base. You can get a GEM or two a day from this mine. And while that's nice, it's not nearly enough.
Let us get 2 Gem mines, and maybe a third on the regular village. Or even speed up production with more upgrade options. Of course, we can't get 100 gems a day, or no one would spend real money and the game would run out of funds and development. Supercell could give us just enough to mix things up, make it exciting again, and get upgrades moving like the early days. Combine more Gems with the Books we win from Games, and upgrades wouldn't be so hard.
Those who are willing to slowly save up gems over the long haul could use this to their advantage. Then, like regular gold in the game, attackers could be able to steal some of your gems from Gem mines. We don't have a Gem storage but attackers should be able to earn a few. This could even give players an incentive to not only use them but attack when someone is sitting on a pile of gems.