The current rich text editor is good - but it could be great.
The ability to insert a table would be ameliorable
The ability to insert a tweet would be sweet!
The ability for the designer to/editor to restyle floated images in mobile - i.e. make images 100% width/don’t float them for mobile landscape and portrait mode.
We could embed Tweets in the RTE if it was supported by Embed.ly, because the embed feature of the RTE is built with Embed.ly tech I’ve heard.
http://vincent.polenordstudio.fr/snap/m998f.jpg
So potentially you can emebed all those services:
But it has to be tested. For instance I could embed a public Facebook post.
I’ve tried inserting a public facebook post and a tweet using that embed option but neither works 
Twitter is just not supported by Embed.ly. Facebook is said to be and test results on the site work. But Fb is notoriously chilly regarding external embeds.
This would be awesome. Currently we have a work around by using the dynamic embed feature and replacing the twitter/facebook/instagram url extension in our blog collection. It’s ok for now, but something within the rich text field would be ideal as we can only have so many twitter/facebook/instagram embeds due to the 30 element max in collections.