Bit late to the party, thread had gotten unwatched...
Saying the bigger packs offer more longevity is also a fallacy. If I put BnB and Monster side by side (all mods enabled) then BnB takes an average of 4 times longer to reach endgame. The only reason it is not more popular is because it is (afaik) the most difficult pack currently in the public eye.
BnB has 1/8th the user base of Monster and rising. The only reason its not more popular is because the mobs and such are to hard for casual players.
I am sorry to say, but I think you are judging us all on a rather narrow/biased point of view. Personally it I am simply not interested in the BnB, Magic Farm 2, etc. packs due to its narrow modlist and the fact that if I wanted to play a action/survival game(which I often do), I would do it in something other than the clumpy MC engine. I play MC to build stuff, and as such I want lots of mods to facilitate that. Maybe some of us simply do not want to be gated through stuff through quests or be harassed by mobs when building at night.
And how exactly do you define the "longevity" of a pack as the time it takes to reach "endgame"? Do you intend for people to just stop playing a pack like Monster once then reach this so called "Endgame"? I can see that the purpose of one of your so called "hardcore" packs would be to survive until the endgame, but for me the endgame is just the first threshold to allow me to start building huge and advanced stuff in the large modpacks.
I guess we would be ok as long as we can be assured that creating our own packs is really as simple as clicking somewhere to combine packs or tick mods off somewhere to add them, and then everything then just works with configs etc. And that server owners can easily distribute the packs they have been forced to customize to their players in a simple and easy to understand way for everyone(even the least computer adept player). If not, then there will still be a need for the large modpacks and if FTB chooses to no longer supply them, then I can only see the option for people to go elsewhere.
It is quite clear that you and Jaded are much more interested in making your own more specialized packs (To such a degree that it seems some of the official FTB packs have become quite neglected IMO). But would it not be possible to recruit/hire/whatever someone to continue the tradition of the "large builders paradise" packs?