Disclaimer: I know this will not happen due to corporate greed (not just MS, pretty much all AAA games in 2017+), but below is my dream scenario for Halo 6
A complete, polished campaign, arena (social (including native BTB & ranked)), FF (not WZ FF), and whatever new mode is introduced. A legit theater, forge, custom games options... Basically a polished version of everything we have come to know and love in Halo (not going to list everything).
Nuke the REQ system, only well thought out meaningful armor / helmets, including many that can be earned with different activities or achievements. Advanced customization like Reach.
All users get all of the DLC maps for free.
So, there would have to be a healthy source of income for 343 to have a business case to continue to support Halo 6. This is where it gets tricky. I would like a combo of cool things to buy for Spartan ($1-5 dollars each) like back in the day for in game and avatar gear, and a Reach like credit system that people could 'buy points' to ultimately unlock the cool armor pieces / effects faster (but also grindable). Basically like REQ, but change to credits and have it spendable like Reach. Also, make everything that can be bought with credits straight up buyable with cash (so not RNG like REQ). Want the cool lightening effect? Grind that 1,000,000 credits (or whatever) 'OR' drop $4.99 right now and its yours.
Of course, all earn-able gear (like recon - vidmasters - achievement based) can NOT be bought with real money or credits (until unlocked by performance requirements).
I honestly think this would make more money and also keep fans happier.