IME, most people balance player options for their limited experience, no matter how much they intend otherwise. For that reason, I'm not interested in paying for anything in that vien that isn't heavily vetted by playtesting with a broad base. My games vary too much in numbers, style, and tone, and I hate multiple sets of allowed homebrew and houserules for different campaigns.
So, that said, I'd love to support NPCs, gaming aids, dungeon dressing (bookcases, chests, doors, tables, etc), MAPS, flash fic/vignettes exploring locales and scenarios and factions, etc, NPCs, common magic items of no particular power, encounters (adventures are cool, but I only grab them to loot their encounters/locales/basic hooks/factions/NPCs and place them where I need them), and other such support material.
The only player options I'm interested in is stuff like simple and useful systems for inventing, alchemical items, and other expansions of the mundane and semi-mundane adventuring gear and group resource stuff (like airships), that wotc doesn't really support at all.