I knew there was one I was forgetting: Armed by David Ratliff (written for a previous version of Inform 7; it wouldn’t compile with the modern version without changes).
I think this hasn’t happened 'cause what you’re abstracting how and at what level of granularity stands to be so wildly different between any two conceptions (he says someone who has learned a bazillion RPG combat systems). Also, once you know Inform, it’s fairly straightforward to write such a thing – the harder part is designing the combat system, not the coding – so people haven’t had much incentive to not just start from scratch.