Please ad Mastodon to list.

I would love to be able to add Mastodon to my site's footer from the ACP. Any update on this, will we be able to do this in v5?

This is not in the current 5.x alphas. 

Fully agree, Mastodon / the Fediverse grows slowly but steadily!

Would also be great to have "Share links" to Mastodon

I just discovered that there is a Mastodon icon in the icon package that IPS uses in v5, so it should be fairly easy for them to add Mastodon to the drop-down list in the ACP. 🤔

I've added it myself, see image above (hover effect).

You can add it yourself.

Copy the code below as a "hook" to your template (see image below):

<a href="https://mastodon.social/@USERNAME" target="_blank" class="ipsSocialIcons__icon ipsSocialIcons__icon--mastodon" rel="noopener noreferrer"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><path d="M433 179.1c0-97.2-63.7-125.7-63.7-125.7-62.5-28.7-228.6-28.4-290.5 0 0 0-63.7 28.5-63.7 125.7 0 115.7-6.6 259.4 105.6 289.1 40.5 10.7 75.3 13 103.3 11.4 50.8-2.8 79.3-18.1 79.3-18.1l-1.7-36.9s-36.3 11.4-77.1 10.1c-40.4-1.4-83-4.4-89.6-54a102.5 102.5 0 0 1 -.9-13.9c85.6 20.9 158.7 9.1 178.8 6.7 56.1-6.7 105-41.3 111.2-72.9 9.8-49.8 9-121.5 9-121.5zm-75.1 125.2h-46.6v-114.2c0-49.7-64-51.6-64 6.9v62.5h-46.3V197c0-58.5-64-56.6-64-6.9v114.2H90.2c0-122.1-5.2-147.9 18.4-175 25.9-28.9 79.8-30.8 103.8 6.1l11.6 19.5 11.6-19.5c24.1-37.1 78.1-34.8 103.8-6.1 23.7 27.3 18.4 53 18.4 175z"/></svg>
<span>m</span></a>

Then just add this code to your custom CSS:

.ipsSocialIcons__icon--mastodon {
  --_brand: #6364ff;
}