Dead Money (Reference to future Story-Arc) : NPC speaks about the Last DLC and the events of what happens in it.
Honest Hearts (Involves Joshua Graham, New Canaan, Caesars Legion): Joshua Graham supposedly lives, and you decide to travel with Ringo/Merchant (Depending on the choice in Goodsprings.) to help start a branch in New Canaan, and along the way you meet Joshua Graham (Supposedly dead.) and he would MOST likely want revenge against the Legion, so what I speculate with this is that you either help him take revenge, change his views to accept what the Legion did for the good of the Faction, OR kill him. (The Grand Canyon, Possibly the Great Divide which is involved with the supposed Last DLC.)
Honest Hearts is tied to this DLC from Grafitti in the game, nothing I can tie from a speculation.
Big Empty: It may involve Tibbits Prison/Research Base (Van Buren.) which would be known as "The Big Empty" which is referenced by two NPC's in Dead Money and content from some scrapped ideas from the Cut-game Van Buren, Alot of old Pre-war technology is said to be there, It's possible that it may involve destroying the base, or preserving it.
The Fourth: Python- Helios One: Python is hinted at by devolopers to have more than meets the eye, possibly related with a Poseidon Energy based DLC- Possibly involving the Enclave or a Powerplant.
Lonesome Road(?) (Going southwest.): Mojave Outpost is most likely involved with this possible DLC, If it is, judging from the map of the world then the MOST likely area for it to take place is The Hub, you may leave the mojave to work as a Caravan Guard seeing that the Mojave Outpost is a checkpoint for Caravan's, and that the Crimson Caravan is headquartered in the Hub.
Possibly involving Raiders (Old fashioned.), the criminal factions, or the thieves guild.
The name Lonesome Road is tied to this DLC as it seems to be a reference to a Caravan raid, The Courier being attacked with a Caravan, being the lone survivor, being on the lonesome road.
Old World Blues(?): It would be the DLC with the Courier, Involving Ulysess, The Great Divide (Speculated by many to be the Grand Canyon.), the possible things involved might be involving Boone in which you would have to decide between him, or Ulysses as Permanant companions, or as another scenario, You would have to help Ulysses fight someone (He is supposedly CL, so it may involve attacking the NCR.) or defend whatever it may be he fights against. (Which would mean you fight against him.)
The name is tied with this DLC as Ulysses has the flag of the Old World on his back, and seems to be fighting for what was once America. (Blues being related to the Courier and his struggle perhaps.)
Courier-Ulysess relation: Worked together before/Minor Encounter.
Someone has took note of Zeni-max purchasing the titles for somethings that seem to be related to Dead Money, I updated them to show which DLC I think they are tied to.
Judging from locations in-game, and inclusion of open-ended content, I feel there will be six DLC's.
Thoughts on my reasoning and speculations?
Van Buren DLC/Final DLC
Nothing much is known about this DLC, I've just found out about this DLC...
This DLC would feature an area we would never expect to see according to a source. It is said that a personality from Fallout 3 is going to be featured in this DLC as well...
Possible Unexpected Locations: A.) BOMB001: Cut-endgame location for Van Buren. - B.) Tibbets Prison: Cut start from Van Buren.- . C.) Vault 13
Possible Fallout 3 Personalities: A.) Augustus Autumn, B.) Eden, C.) James