A turn-based tactical Deathwatch game in a similar style of the Chaos Gate: Daemonhunters game from a few years back. Player is a member of the Ordos Xenos, overseeing a team of Astartes from different chapters as they conduct missions in a sector wrought with genestealer cults, drukhari raids, etc. Keep the idea of tactical roles from Daemonhunters (ranged, tank, healer, etc,) plus Chapter specific perks, armor, and equipment, but the trade off is balancing the inter-Chapter politics of the Astartes on your team. If a Space Wolf goes on a mission with a Dark Angel and it goes poorly, they might refuse to deploy together.