could it be that you're thinking of minimalism in the wrong terms? i don't play a lot of true roguelikes, but i think the pleasure in something like xcom is in looking at a large, complex game state with many actors and trying to determine what will happen next and how i can influence it best. the classic "lessons learned the hard way" page on nethack wiki is of this flavour when it's not about battling the UI -- arcane interactions between mechanics that require the player to have both knowledge and theory
so maybe a minimalist approach that tries to really drill down to just this notion would be something like chess puzzles -- remove all the normal context, the campaign, the bloody sokoban level -- show the player a "snapshot" of the game and ask them to make the best move (or perhaps even just to predict what happens assuming ideal play). dude... chess puzzles are kinda like wads, dude -- though the problem with this of course is that most turn-based games have some degree of random variance
designing for this would require walking a fine line when it comes time to decide what units can and can't do -- particularly how much "reach" they have and how many interactions the player has to think about at once. but this sort of thing isn't my forte, just a thought
