I didn´t give my reasons for the rankings, I was gonna edit but I will post here:
1.-Reborn! It sells well, it ranks consistently good enough not to be cancelled, has a stable fan-base and for what I know it can be stretched for years to come.. So why did I rank it here?
Solely for a reason:
The anime ended and while Gintama´s anime adaptation end too it had a continuation, the sells for the tanks are good yeah I know but the lost of the anime, now I don´t know how well it sells or how its story is going (I don´t read it) but from what I have read of other people´s opinions the story is being stretched.
Still the fujoshi fan-girls will probably make my prediction turn out to be false.
I give it a year and a half. 40-45 Volumes
2.-Bakuman Its a very interesting, entertaining, very-good selling manga, then why? Because of the authors history of mangas, they tend to have medium sized works, IIRC Hikaru No Go is Takeshi Obata longest serial and the premise of Bakuman itself.. I mean I just can´t see this manga lasting longer than 25 volumes, it currently has enough chapters worth 16 volumes (well 15 and a half) and using my logic of this manga not being possibly longer than 25 volumes then I give it 2 years top to end, simple as that, obviously it won´t be a cancelation but an ending, likely an open-ending kinda like Hikaru No Go (I know the mangakas are different writters for both series but Bakuman seems like the kind of manga that will have an open-ending).
2 years from now it should end. 20-25 Volumes
3.-Nurarihyon no Mago Currently with a second season it has at least support for half a year AT LEAST, but something strikes me of this being cancelled, like it not being able to really pick up on sales and JUMP deciding to cancel it so that the mangaka makes a new manga.
Mago has 2 years left in my opinion. 25-30 Volumes
4.-Medaka Box If it weren´t because of its anime adaptation I wouldn´t even had included this in the list, anyway I think the anime will give it a little boost, nothing too big and it will end in around 2 or 3 years.. Thinking things straight I should probably have put this at number 2.. I can see this canceled half a year after its anime adaptation by being low 5 in the TOC..
Still the name of the author, T&A and Gainax making an anime out of it.. Should be good enough to promote sells and merchandise.
As I said in this post, rethinking stuff I think this might not last that long. However I give it 2 more years. 20-25 Volumes
5.-Naruto I hope this is the last arc, sadly the war has turned a way I predicted lonnnnnnnnnnnnnnnnnnnnnnnnnngggggggg agoooooooooo.. Like back when Orochimaru first used you know what, I said to myself "This technique is too uber.."
Anyway, Kishi could continue this for around 2 to 3 years. 70-75 Volumes
6.-Gintama As Kaiten said, apparently Gintama is very, very liked, when the anime concluded the fans were sad.. Sunrise response was a "Best of" a movie and then continued the anime, I have not heard/remember of any JUMP manga or (any other) with a similar situation, besides Yu-Gi-Oh! but that was different, different companies involved and the series was way different from it first season..
What I am trying to say is: Gintama is popular, its episodic (That´s one thing Reborn! doesn´t have going for it!) has an anime (Reborn! doesn´t) it could be the next Kochikame, in fact IIRC it sells wayyyyy better than Kochikame, no?? I mean Kochikame doesn´t actually sell that well but its a staple because of how long it has been, right?
My prediction is based on something I read saying Sorachi wanted Gintama to last 30 volumes.. So far there is around 43 volumes worth of material so he has exceeded its expectation by 13 volumes.. So what ONE PIECE has by like 35 volumes!! (And will continue) Anyway I think Sorachi didn´t intend to make a loooong series yet Gintama managed a stable fan-base, a continuation of its anime, a movie adaptation, very good sales and its still strong.. TL;DR its hard to predict, but I say.. 3-4 years. 55-60 Volumes
7.-Sket Dance Seems like a Gintama with less popularity, not bad at all but not as popular. 3-4 more years. 30-35 Volumes
8.-Bleach Lets imagine 3 scenarios.
-Good: It gets better and its anime continues. I don´t think sales will get better, In fact in the best of cases I would expect them to either stay the same or drop a little bit.
-Medium: It continues being shit (IMO) and the anime continues. The sales will probably dimish slowly until around 400,000-500,000 per volume.
-Bad: It continues being shit (IMO) and the anime ends. This could spell DOOM for BLEACH yet I think even without its anime adaptation it could still be suppored by JUMP at least for a while so that Kubo ends it in a "natural" way, its volumes sell less by each volume reaching low marks of 300,000 or so volumes (Which is pretty good but not BLEACH good)
I think I am going to go with the Medium scenario, I don´t see BLEACH getting better or even getting to the level it once had back in Soul Society, now its all about cool poses and Bankais and battles and Aizen trolling, scratch that actually..
5-6 years. 75-80 Volumes
9.-Beelzebub. Its just a feeling but I think Beelzebub is gonna be the next JUMP big thing, I mean I haven´t even read nor watched the first chapter/episode, I know barely nothing about the series (Except there is this naked demon-child being taken care of by a punk) nor I have the volume data, and I know the comercialization in other regions of the world is gonna be though because of the baby being naked.. But God I saw this avatar of the baby Beelzebub (Is that its name?) with a Oudan suit.. He looked so badass and funny LOL! and I said to myself "This is IT!"
Also the reason I don´t read "new" Jump mangas is because I get "heart-broken" when they get cancelled, I am a simplistic folk, I tend to like over-the top, generic mangas, I liked how Metallica was turning (Kinda like HXH IMO) and KO Sen was good IMO then.. Well we know what happened. Maybe its about time I watch some Beelzebub.
6 years. 35-40 volumes
10.-Toriko Toriko has been marketed as the next big thing practically since chapter 1, it better be LOL.
8-10 years. 55-60 Volumes
11.-One Piece Its ONE PIECE, the manga that literally outsold the combined TOP 9 property mangas.. It can continue lots of years.
15 years. 130-135 Volumes. Also as a extra prophecy of mine: I think ONE PIECE will get published in 2 different Shueisha magazines at the same time in the future, It will still have its weekly chapter in WSJ but the same chapter will be published in other Seinen Shueisha magazines the same week, something like that, for readers of Seinen magazines that grew with ONE PIECE