The reason contacts don't tend to show up on Matrix/Element is because we don't push the user into sharing their addressbooks given the obvious privacy issues. Instead you mainly have to figure out who you know out-of-band for now (e.g. tweet "hey, who's on Matrix?").
I would be happy to have an option to share my availability on Matrix with other people that decided the same if that would mean I could bootstrap my network on that platform.
As it is now, Matrix may offer better privacy and more robust weil federated and p2p, but if I had to personally ask all of my contacts if they actually use it using some other medium, I can keep using that other medium too for conversations.
