This has been implemented and is now available.
Just use a colon followed by a shortcode followed by another colon, for example: 👍
As @newtboy requested, there is a 🤦 emoji and thousands of others, and as @ant requested, they are rendered as simple standard emoji characters.
If you hover over an emoji, you'll see the shortcode text that was used to create it.
The full list of emojis is available on the following page. Click the emojis you want and then copy them all to your clipboard by clicking the 📋 in the bottom-right corner, then just paste away!