True, but it's still cluttered. If I want to see who my friends are I can look at my friends list. But it's pointless to argue since a good compromise would be to have everyone who is online be showed at the top :-)

Don't get your point:
You would need to know WHO is WHO anyway - regardless whether a user is off- or online.
Remember that the right column list already contains your friends only - not every member.

Aside from that: At least on a PC you may hover those user icons to get first and last name.

Ah, good I could be of help then :-)

I understand that point of view, but then you still need to know what profile pic that person is using, or you might just as well use the search function. So being able to see just your online friends still makes more sense to me. Would it be difficult to do?

Good that you asked, because intentionally online friends SHOULD appear on top.
But I made a mistake on implementing, and only new arriving friends appear on top while all those who were already online when you log in are listed at the bottom. This issue will be fixed with the next release.

As for displaying online users only:
yes: basically possible, but you might want to send messages to offline users, too, but you can't do so any longer if there are no more clickable friends icons in place.