Twitter is not trying to be the next Facebook. Twitter users adopt the platform to make constant updates about what is going on throughout the course of their day. Facebook users are more concerned with staying in touch with people they are close to, chatting with them, and posting pictures about the events in their lives. These two sites have totally different aims.
Twitter is targeting a totally different used than Facebook. There goal is reach the user who can fully express they message in 140 characters or less. In many cases Tweets are used to connect followers to different a web site or other Internet destination. Twitter is already very much a mobile app while Facebook is still trying to define its mobile appearance.
No, I do not believe that twitter is trying to be the next Facebook. Twitter has a different way of communication. Twitter is more of an instant message type communication. Both have ways things can be commented on but I think that they have two very different avenues of approach in social media.
With the ever expanding profiles on twitter, people are beginning to equate twitter to facebook. The only way I would accept that is in the form of profile expansion and the recent addition of photos in messages. Even those photos stick to the script of short and sweet messages. Facebook allows for lengthy conversations and posts. The information stored and distributed through Facebook is much more comprehensive. Twitter is made for the ADHD society that wants a quick message that gets to the quick and dirty of the situation. Facebook requires a bit more focus.
Twitter and Facebook can both coexist in the same Internet space. Both have marketing prowess and both have hundreds of millions of users. Twitter has much different operating parameters from Facebook. Both keep people connected in simple ways. Both rely on quick communications. Both are able to post pictures and messages from cell phones. Yet Twitter is not trying to be like Facebook. If it does, that will be the end of Twitter as we know it.