WildFly 11 should support JDK 9 but it seems that DevStudio don't count with it. It is not possible to choose WF 11 as a runtime when Java 9 is choosen in project facets.

Try this:

• Install and run JBT or DevStudio against Java 9
• create Dynamic Web Project
  • choose WF 11 as target runtime
  • click Finish
• right click on created project -> Properties -> Project Facets
• note that it is configured to use Java 1.8, not Java 9 and you are not able to select Java 9.
• open Targeted Runtimes tab
• deselect WF 11 and click Apply
• open Project Facets tab
• now it is possible to choose Java 9, so do it, select Java 9 and click Apply
• open Targeted Runtimes tab
• Wildfly 11 isn't available, it is hidden.

The same problem is with Dynamic Web Module 4, it is not possible to use it with WF 11.