I saw a rumor it would be “through the usb c port,” which suggests 2018 pros only. But not having corded mouse support and not bluetooth mouse support would make NO sense, so I think the other iPads will get it.
It’s possible. Mouse/trackpad support is 100% coming as an accessibility feature, but we just don’t know which devices and how it will be implemented. I can’t see them going with a wired only solution, that would be quite the opposite of everything they have done the last few years.