The landscape, foliage and mesh paint tool code still supports a pressure value, and in the case of foliage it looks like it’s recently been reconnected for VR controllers when the editor is in VR mode, but unfortunately the UE4 input system does not currently support getting pen/tablet pressure data.
We have a ticket UE-16596 to add this support, but it is marked as backlogged and so it doesn’t look likely that we will be able to allocate resources to this any time soon.