I'm cool with both styles for Batman. Batman Returns really pushed the limits in terms of the fantasy elements with Penguin and his army, and Selina being able to come back from the dead more than once. I recently watched it again after many years and it still holds up quite well. It's quirky and silly in a lot of ways but I still enjoy it. I get where you're coming from though in terms of the "realism" and grounded take on things. I think Batman is a story that can play in either world of ultra grounded or fantasy and it can also tread the line deftly between those two extremes. I personally always adored the Clayface two part story in the Animated Series and would LOVE to see that translated into live action.
What I'd like to see more of is to move away from rubber Batsuits, overdesigned military amalgamations, overdetailing, and dye sublimations. I just feel there are so many superhero costumes now and often times they are more ornately detailed than they really need to be. They're great costumes, but it would be refreshing to see traditional textiles used in new ways. If they set it in the past (WWII era) and approached it from a grounded story/ world, I always thought it would be super cool to see a 1940's style film noir type suit where he's using pre and post war military surplus gear. The boots could be modified paratrooper boots, the cowl a modified helmet with aviation goggles. Either leather ammo pouches or canvas web belts/ ammo pouches for the utility belt. The cape could be a modified parachute. Design wise it could borrow from real elements to set it in the era of the 1930's 40's but they could be changed to suit his needs for crime fighting as a bat.