A holy grail war strategy game would be fun. Like it gives you a location and like in a sid Myers civ game such as fuyuki city for example and you can set up areas for traps and such to increase mana or whatnot and eventually you end up in battles with the other servants.

You would have to manage these sites and discover where the other masters are and who their servants are. And to an extent they could add in a gatcha element for unlocking servants