Not a bad thought. Maybe Niantic will make something of it. Or maybe you could, once a day, do a solo raid where you pick the boss, and get a better than normal reward for that boss type, like a level 25 or 30 mon, more stuff, etc. And that way, you could pick almost any mon - want a level 30 Pinsir? Beat the solo Pinsir boss.
Hope Niantic is listening in here.