Seeing how well Mastodon is doing makes me want to finish a similar project I started a while back.
One basic thing I see that could be added to Mastodon is meta data being pulled in from a Gif link.
Not too sure about doing it with web links as it might become too spammy like.
If Mastodon's backend was built on node I would look at contributing a good deal.
Creator of things
The original server operated by the Mastodon gGmbH non-profit