Will cargo already affect flight in the ships in 3.0 or not?

Not right now. There's a little bit of game code to get the mass applied from the cargo grid into the ship and then to have IFCS after that use that information to make it require maybe more thrust in gravity, but not in space. So it won't in 3.0, unless it suddenly gets added. But right now, not planned. But that is something that I've heard come up multiple times, and it's definitely on our radar.

We've spoken at length several times. That is a good example of a feature that we want in the game that will make its way to the game, but is not present in 3.0.