This has been covered already in a few places, like here:
As also shown in some other places - you dont have to remove or disable synaptics. You just wont be able to use the plasma settings to configure it.
As to specific issues with libinput:
There arent any.
This is something that can be provided by an application if it so supports it.
For example - firefox. I use libinput and have kinetic scrolling in my browser (but not the terminal).