I've been a fan of the civilization series since II. However I haven't played all of them due to being busy at different points in my life. Didn't play VI for example, but I did enjoy V, some of the DLC for it was good IIRC.
I'm concerned about the pre-order push, and that there is going to be a Switch version. But it does look like it could be good? No way I'm pre-ordering, but would like something to look forward to.
I don't think they're implementing co-leaders.
They've decoupled the leaders from their historic civs - such as having the ability late game to have whatever woke Cleopatra substitute they have this iteration leading Mali or Mongolia.
The social progress leader stuff is more that they've announced that leaders don't have to have historically led their nation anymore. The example they gave was Ben Franklin leading America.
This is an obvious ploy to stick as many female and indigenous characters into the game as possible because there simply wasn't enough historic options with the old constraints.