I've always thought that there should be some penalty for being a warmonger, such as a negative diplo modifier or something. Civ 5's method is too harsh. I'll wait to see if Civ 6 has any better system. If Beach is saying that there is a minimal penalty in the early game, that might give players an incentive to do early rushes again. I don't think they were feasible in Civ 5. At least I was never able to get one to work. City bombardment and enemy units would take out my units long before I could take the city. Granted, I'm not the most brilliant Civ 5 player around.
Something that I would like to see is an AI in Civ 6 that can take your city if your unit goes wandering about and leaves it unguarded. You know how in BTS, you can start with a warrior instead of a scout? Well, if you send your warrior off to explore, leaving a city unguarded, what is to stop an AI warrior from taking your city? Nothing really, except that the game doesn't do it. An AI warrior can waltz right past your empty city and ignore it. I've been trying to make the AI declare when it finds an empty city a reality in Better BAT AI, but so far I haven't had much success with it. If Civ 6 has such a mechanic, though, it might be a good thing. It would certainly curb some forms of exploration, and it would be more realistic.