Drush that comes with AcquiaDevDesktop2 (Apr 13, 2017 release) is unusable with drupal 8.4 as it uses symfony 3 components unlike earlier versions of Drupal 8.
For you to use drush with Drupal 8.4 and upcoming version you will need to update drush (focusing on those who use AcquiaDevDesktop for local development). To do this (windows users) locate the directory for you installed AcquaiDevDesktop and move into tools folder.
In my case it was 'C:\Program Files(x86)\DevDesktop\tools' , edit the composer.json file and change, "drush/drush": "8.1.8" to "drush/drush": "9.0.0-alpha1" and save (you made need to change your directory and file permissions to do this). Note that 9.0.0-alpha1 is the current stable version as of the date of this article. Open your cmd and move to the devdesktop tools folder.
In my case 'cd C:\Program Files (x86)\DevDesktop\tools' and run 'composer update'. Make sure your internet is on. Thats it you have drush 9 in your local dev environment.
That was my question and How I got it to work?