This topic has been discussed quite a bit already.
The mod you refer to has the luxury of being a mod.
If we wanted to extend post-endgame sequence, we have to deal with the fact that one of the three major factions in the game is gone. Not just depreciated, but actually *gone* from the game world. That means that every single quest and NPC that references that faction has to be modified in some way. This isn't like Fallout 3, where we can just excise the Enclave from the world and everything's fine. The entirety of Fallout: New Vegas is affected by post-endgame content.
But again, that doesn't matter for a mod. That's why mods are great. They don't have to round up every single actor and record new dialog to explain why you can't complete a quest anymore. People won't complain about that. They won't complain when you go to a specific area and there are NPCs from a faction that shouldn't exist any more. But if you buy an add-on, you expect those things to be there. And think about just how much that entails in a world the size of FNV, and just how tricky that would be to do.
Alternatively, we could do DLC that takes place long after Hoover Dam, in a mojave that is vastly different. But people wouldn't like that either, since they couldn't continue their existing quests they started before the endgame sequence.
In other words, the only way we could do post-endgame content is to do it really poorly. So we decided not to, and instead focus on the DLC we're releasing.
You may not like this decision, but surely you can understand why we did it.
I still think that a DLC where the Courier returns would be good... people always say, ahh thats stupid. When its not official, but when it becomes official, people suddenly think its a great idea. If i remember correctly, alot of people freaked out about open ending fallout 3. People bickered back and fourth, but when Broken Steel came out, most were happy with it.
The same could be said here... so what if they can't do the quest they did before... i say just reload for that. The thing i don't like is having the quest cluttering waiting to be complete in my quest list. That and i always hate feeling like there was so much more i could have done... and thinking i rushed the game, even tho i completed 80% or more of the quest.
Mainly the major thing i want to see, it dosn't have to open end the game, but in fact what i really liked about BS is the fact that the wasteland changed, not just one area, but every area, well almost every area. I want these DLC's to have more effect on the Mojave itself, yea a few new weapons in the market is great and all... but i want changes you can see.
But as i type away, it may sound like i don't appreciate these DLC's... Far from, i love them, and New Vegas is my favorite Fallout game, i think it was done very well. And i know you pulled alot of resources into the game, which is the reason for all the lag. (Which on the PS3 i always get in Free Side)
The DLC's are also very entertaining, but i feel like the best is yet to come. OWB looks amazingly fun, and i just hope you payed attention to some mods, as i heard you guys do. Hopefully that Project Nevada was brought up, because i love the implants, and am wondering what implants you might add to OWB. (Yea i watch videos of mods... getting jealous at not having a good computer)
But as i said, if you can make the DLC's do a little more to the Mojave, rather it be getting a new companion you can bring with you out of the DLC areas. Would have loved bringing that girl from Dead Money, found her pretty cool. Maybe add in dialogue that mentions some of your accomplishments in DLCs (If there is non for Lonesome Road i am gonna kill someone, obviously its a widespread story as the ending for Dead Money they all mentioned the battle at the divide.) So i hope people will talk about that, even if its just the... "Aren't you the one from that story" or something like that.
Either way, great job... and keep up the good work, thanks!