Even if Epic isn't directly suing them at this time, a ruling against Apple and/or Google for their store behavior will hit every other app/game store operator. Arguably, there's limits to how many companies Epic can go after at once, and they have to pick their battles somewhat politically, I imagine. But if an Apple or Google behavior gets ruled unlawful in court, and Sony or Microsoft or Nintendo is doing it, Epic probably won't even have to sue to make them drop it.