Twitter announced several upcoming changes to the format of the Tweet and how tweets will be treated in the future. The goal is to open up more characters to be used in the tweet itself.
When you reply to a tweet, the @USERNAMEs will not count as characters in the tweet. The limit will be 50 mentions in the tweet, and all of those names will not affect the 140 count. Also, the dot-mention (.@USERNAME) will no longer be needed, your followers will see all of your new tweets that start with a username (note that this does not pertain to replies, just new tweets that happen to start with a username). If you want your followers to see a reply that starts with a username, you’ll be able to retweet the tweet.
Media attachments will no longer be counted as characters.
Retweet and quote yourself
Twitter will allow you to retweet or quote yourself in tweets. This is the workaround also so others can see a reply.
Over the next few months Twitter will be rolling out these updates. Developers will need time to incorporate these updates into the various Twitter apps, so it will be awhile until you see them.