its not on a public schedule as far as im aware. sometimes you get 1 or 2 in quick succession and other times you see them spread out more and then a bigger content update here and there.
nope not that im aware of like i say no public schedule. you just get a !!!supprise, heres some new cars!!! kind of thing. Personally i dont like roadmaps and telling all, i like the supprise and there is no "but you said this would be then, and your already a week late delivering it, you suck devs!" - that you get with all games with a public roadmap. So i dont reall want to see one.
not sure how I feel about that - the suprise is cool but also nice to see the devs are working on something and not deserting
just look at past updates and how often stuff is released and updated. there is no deserting the games been going years constantly updated and you can browse the forums and interviews here and there and see they are always changing and tweaking stuff.
To get an idea of what is planned at some point in the future there have been a few posts over the last couple years (maybe 1-2 per year). This should be the latest one from last summer: https://forum.sector3studios.com/index.php?threads/summer-2020-dev-notes.15533/ A lot of the planned stuff wont have a specific date for release tho so its just a broad overview and not quite a real roadmap