Just as expected, more information about the upcoming Galaxy Note9 starting flowing in and latest we hear is that the Galaxy Note9 will allow you to use DeX mode without the DexPad, instead, you can use it just by connecting a USB-C monitor or HDMI.
Furthermore, the Galaxy Note 9 and Tab S4 are expected to pack a feature called Dual Mode and this will allow you to simultaneously use an external screen and your smartphone or tablet screen. The screen of the mobile/tablet display can be used as an extension of the main one that can perform different operations like Chatting on a phone while watching a movie on the monitor.
The next version of the Samsung DeX will also support the S-Pen for the first time both as a mouse to point the position on the screen and drag elements, both to draw or write in certain applications. Back in November 2017, Samsung described that it is working on Linux On DeX that will let you one or even more Linux distributions in DeX mode with a real desktop environment. However, it is not clear if the Note 9 will have such function or is it limited to Tab S4.
The Galaxy Tab S4 will also get the DeX mode and it can be connected without an external screen. In a way, it counts as a true desktop interface.