Batshit crazy idea of the month: hear me out.
Apparently H5 is peaking somewhere around ~100k concurrent users (prob closer to 125k), which isn't horrible but according to this thread
http://www.neogaf.com/forum/showthread.php?t=709697 its lower than H4 which is understandable (lower install base) which is disappointing. We'll see what Christmas does.
So alot of complaints were either campaign/lack of content. In 3 years the xbone will have a huge install base (slim coming next year). So release H6 as a F2P multiplayer only game ala Dota, LoL, Hearthstone etc. Thats ~50million people possibly playing H6 in 3ish years. With the game being multiplayer only, it can be flooded with content, huge number of maps, iterate on warzone (incorporate firefight into it?), return/imrpove all of the old features (4 player theatre viewing, firefight, gametypes etc), give forge a huge upgrade (AI/Scripting), you know where im going with this. Include a classic halo playlist or 2 and keep improving the solid gameplay of 5.
Now how do they make money? Go balls to the wall with REQs. I want 50 armor effects from Reach 3$ each, I want Arnold Schwarzenegger to be a MP announcer for $5, hundreds of skins for a few bucks including user made ones, just let your imagination go wild. Customization up the ass. Make it so you can buy them all with RP but it will take a decent chunk of time, or just buy them. Then continue expanding Warzone and its current crazy ass weapons/armor in packs thing it has going and dial that up a few notches. If you say 343 puts 25% of req sales into HCS which is a solid guess, 700kx4=2.8mil in 3 weeks with sales probably around 3-4mil, if you take a ~50mil ish xbone userbase that's going to increase it by a factor of 10, not counting all the new cool shit even I wouldn't be able to resist. 2.8x20=56 mil. H5 only had sales of 400m (including hardware) so its not completely illogical.
Development costs will be 1/4th of what H5 was. Do another, bigger "sustain" for this game and you can keep MILLIONS of people around for years (instead of ~125k concurrent). Would be a huge advantage of Xbox. Throw in a possible player economy/esports integration CS/Dota etc use and we could be having massive HWC tournaments rivaling LoL/Dota. Player engagement through the roof.
Of course people love the Halo Universe, playing through those non combat missions it looks like 343 had some ideas but didn't have time. I say make future mainline game SP only ala Fallout/Elder Scrolls, those are hugely popular. Maybe branch off into a FPS RPG focused more on story/universe ala mass effect and way less on loot like destiny/borderlands.
So we would get a MASSIVE multiplayer offering for free, with only OPTIONAL micro transactions that are cosmetic or warzone only, with a huge thriving multiplayer community/economy and us drowning in content (modes, maps, features, etc. even adding AI to forge would create infinite content). On top of that we would get a ~$30-40 high quality Halo story continuation that could literally go anywhere even across genres. (seriously while playing those missions I was sitting there....what if?).
I really think this would work.