Halo: The Master Chief Collection is changing its progression system for the upcoming Season 2 update. Developer 343 Industries announced that it will soon begin to allow people to purchase "seasonal items." [Update: following the publication of this story, Microsoft removed the word "purchase" from its blog post, so it seems microtransactions may not be coming to MCC]
MCC currently has a battle pass-style progression system that players grind through gameplay to unlock new stuff.
Vehicle skins are coming to Halo: CE
"We also heard feedback that players want more choice in the order they unlock items, so we are adding the ability to purchase seasonal items in a given tier in any order that players want," design director Max Szlagor said on the Halo website.