> If there is space for 3.5mm you might have a point.
I don't think you get it. The reason why there isn't any space for 3.5mm now is because they didn't want to add it, they could add the space if they so choose. This is not a problem you should think about, it should be the designer/engineer/etc's concern to figure out how to fit it in.
It is normal for there to not be any space in portable electronics, that just means they've utilized all the space they had optimally; it doesn't mean they can't add more features and redesign it to accommodate the jack.
I would prefer two USB-C over one USB-C plus one 3.5mm. It would be more useful to a lot of customers.