I’d love to see this in OF3. The Sorted 3 app does seem to have a smart scheduling feature. You might want to try that app out.
I’ve used a mixture of OmniFocus 3 and Apple Calendar in day or week view to schedule my tasks. But I do have to do some manual pushing of appointments to move my tasks around in Fantastical.
It works for me but it might be not as cool as auto scheduling. Sorted 3 has that feature going for it.