Just to clarify when I say Casuals I don't mean people like heckfu. Despite his playing habits I think its pretty safe to say he has a deeper interest in Halo than the average Joe.
By Casual i mean players that either only entered this generation with the call of duty franchise or people who played some xbox back in 2004 with some buddies and bought a few EA sports and GTA games since. These people make up a huge percentage of the gaming audience but they are fickle and only care about the next call of duty release. They should never be the target market for a game because no matter how brilliant the game is the chance that they will flock to it or more importantly stay with it is very small.
Sadly you fuel the hype train enough and its going to pull large enough Day 1 numbers to make it attractive for publishers.
Gaming currently is in a poor position because it grew too big too fast with Call of Duty and The Wii and now Publishers are trying to appeal to 10's of millions of people at the same time which ultimately means the products delivered have to be suitable for mass markets making them easier, requiring less skill for accomplishments and more devoted to pleasing people who are likely to drop the game after a month.
Halo 4 is the perfect example of trying to make the series more friendly to this userbase and you can see the negative effect its had on the game and its population. Halo is pulling poor numbers because the crowd it was aiming for did not care and the crowd it had hated the changes made. Its not going to change either. Halo 5 is going to another poor showing with a few legacy features reimplemented so we shut up but things that are ultimately detrimental to the core gameplay like loadouts and AA's and sprint are going to stay.
A major problem is that 343i have already acknowledge that people want zero sprint gametypes with no AA's weapons on map and static spawns and yet are simply not making moves to push them out to players.
I'd wager in favor of population growth if they implemented
Legacy Map Pack (The Pit, Lockout, Midship, Warlock, Sanctuary)
Classic Slayer (No sprint, No ordnance, No loadouts, No AA's 110% movement)
Classic Objective (same as above) (CTF, Assault, Territories)
I'm not talking immense growth but I know a handful of players who would be more than willing to play it again if the above was implemented.