I think MS can afford 1 Halo and 1 Gears per generation; considering it's 6-7 years per generation.
I don't have a problem with Gears and Halo continuing as long as it's not at the expense of getting new game series. If my choice is get another Gears and another Halo, or get two new franchises, I'm going to pick the new franchises.
If you look at their studios, you have Ninja Theory, Playground, Rare, The Coalition, The Initiative and maybe Turn10 that are equipped to start producing new big-budget franchises. I might include Obsidian in there. I know there have been rumours of Playground making a new Fable. They should have the capacity to release new franchises, unless they just tie them up with continuing the series they've been committed to for years.
343 - Halo
Compulsion Games - small studio
Double Fine - small studio
inXile - Wasteland, small studio
Mojang - Minecraft
Ninja Theory - Hellblade 2, bleeding edge
Obsidian - The Outer Worlds, Grounded
Playground Games - Forza Horizon
Rare - Sea of Thieves, Everwild
The Coalition - Gears
The Initiative - something big budget
Turn 10 - Forza
Undead Labs - State of Decay, small studio
World's Edge - Age of Empires
Edit: Added Everwild for Rare.