Master Rank Mantles have slots for decos! Also shown in the dev update is a half-sharpness thingy, maybe a teaser/confirmation for purple sharpness? : r/MonsterHunterWorld
Monster Hunter World | How to Get ALL Mantles & Boosters - YouTube
Mantles | Monster Hunter World Wiki
Monster Hunter World: Iceborne Official Web Manual | Specialized Tools
More decoration slot for mantles at Monster Hunter: World - Mods and community
Monster Hunter World Iceborne Optional Quests Guide - SegmentNext