Splitting by system seems counterproductive.
Where would OSR games go? Into a D&D category? That assumes all OSR games are d20-based and-or retroclones of D&D, which they are not. Split across multiple subforums? That fragments the OSR scene and disincentivises us using the forum.
PbtA is also a nebulous category. Monsterhearts is nothing like World of Dungeons.
It silos off interesting ideas from each other and disincentivises breaking the mould. Some of the most interesting work I've seen lately are PbtA games adopting OSR ideas, or an otherwise OSR game adopting a mechanic that drives narrative toward a predetermined outcome.