Seems like a pretty nice new version of Twitter is being rolled out or tested right now.
They’ve done away with the right side panel entirely and moved your info to the top left:
When you click a Tweet, instead of opening in a right side panel, it opens replies below.
Other person’s Profile
Pretty exciting I think. I’ve always wished for more interesting and sustained conversations on Twitter, though that might be too much to hope for. Even with this update Twitter still doesn’t have a good way of doing threading or keeping older conversations from falling down the feed.