That's a bit difficult to answer. Mostly because I love both Action/Real-time RPG's as much as I love the Turn-based/Strategy kind.
Though I guess it would be something like this: (Wall Incoming)
Steampunk or Victorian-era setting. I was gonna say Western but Wild Arms pretty much cornered the market on that. Well, at least on Western JRPG's (I just noticed how odd that sounds). The gameplay would be a nice mix of Valkyria Chronicles and Final Fantasy Tactics. A very intricate battle system, that takes into account the area around them as well as the enemies, allies and their preceding jobs. I would pick the Valkyria Chronicles view-point with a map option, since I love the flair of it. Instead of moving from place to place on a map however, you would be moving on the land with some kind of caravan (or Airship, Steamship whatever) for all your heroes to reside in and you to plot out it's course. Instead of the whole "create-a-hero" thing, I would prefer Heroes with their own abilities that will be introduced throughout the story or through optional side-missions. The heroes will be able level, and choose between certain Jobs that can be gained from certain prerequisites- learning it in battle, conversation or through some quest. Some characters will have abilities that can affect the environment around them, such as a hunter who could catch and sell game or a explosives expert who can clear the entrance in an abandoned mine shaft. The way you use your heroes and other decisions that you may make would effect the story/ending of the game, without any "best" ending (like Ogre Battle), just a bunch of good or bad endings. The kind of heroes you can get is limited by these same decisions, so you can play through the entire game with two completely different parties with their own strategies. I would also love to have to converse your resources. It would be like Fire Emblem and Oregon Trail. You would have to keep your heroes alive in battle and outside of battle. Keeping weapons in stock, armor in check, enough food for the group, making sure those that are going to battle isn't seriously wounded etc. If they die, well it's that's it for them - and their part in the story.
The storyline would be more about accomplishing a simple task than some grandiose end-of-the-world thing. Something a lot more personal, but could blow out of proportion at times, especially with corrupt government officials or outlaws. The way one would accomplish this task would be the fun part. The story should also involve every character you recruit, so they aren't just back-drops. Your actions should also either alienate or elevate your standings with the group, while also developing your Main Character. Kind of like a Bioware game, except when you start being Paragon you can't just switch to Renegade. How he/she develops would be decided through a few selected traits, class and gender and the actions you make in-game. I would also take the Way of the Samurai route on conversation. Being able to be silent should be an option in certain cases, and in others if you don't respond in time (by talking to say, an impatient person) different things can happen. Situations where you are timed should also have an option to say something like "I'm thinking" if you're talking to someone casually but they are expecting a quick answer.
Stupidly complicated? Yes. My Ultimate Game? Yup. Will it ever get made? Not even in my dreams. This kind of thinking is Peter Molyneux level. I would just settle for just an open-world Valkyria Chronicles clone.