Well, the first update to Blender 2.80 has been released - Blender 2.81. Here
The version I downloaded 2 days ago did not include the latest .babylon exporter which is available here . Open the new version of Blender ->Edit-> Preferences ->Addons -> then find the .zip file you downloaded ( Blender2Babylon-6.2.zip) and click Install. This will give you the 6.2.3 version of @JCPalmer 's great addon.
I also had to activate my GPU for faster texture baking etc.