I'm often busy/lazy so I can't read all tweets at once. So I'm thinking of a new thing: bookmarks. One should be applied to last read tweet, so you know where to continue from (to). Others can be applied manually, to for example last new read tweet* and just something to read later.

Design, I think, should be colorful background for certain tweets and colorful bold stripe between tweets for last (new) read tweet.

* New read tweets are those which get read after updating, are first.
Example:
1) I have 30 unread tweets
2) I read them all
3) I'll get 60 unread tweets
4) I'll read only 30
So, 30 read tweets from latest are new and 30 read tweets from oldest are old. Between them are just unread tweets, oldest has old read tweet stripe and newest has new read tweet stripe. Confusing, but I hope you understand.

EDIT 26.04: Also adding mark as favorite button with star/Pocket [link] icon as I use it to mark stuff to read later.
Wish I weren't so lazy and would actually make them...