The way I see it, Lemmy and the Fediverse as a whole is a big step back to the golden age of the internet before social media became the cancer that it is today and the internet wasn’t controlled by a few big corporations. A big part of that, to me at least, is that you could customize your accounts, home pages, profiles, and so much more. I think Lemmy could greatly benefit from a more expansive profile that lets you customize color, font, design, play audio, and other things like that. I think optimizing the site and adding in more essential features should come before anything like this, but I think it would really enhance the overall experience!
Lemmy like Reddit has many modules.
You have the web user interface.
You have the phone apps.
You have backend that ties it together.
Most of what you is the web page:
https://github.com/LemmyNet/lemmy-ui