Will Drupal be really scalable for my application or site?
We have seen many posts about asking whether drupal is perfect for my application or website. One thing I really want to tell that Drupal is suitable for any type of application or website. Usually people prefer Wordpress over Drupal for developing Blogging sites as Wordpress is fast and easy enough for Blogging sites which is true. Drupal is suitable for you only when your application needs scalability i.e. your application is going to grow in future.
To acheive your goal of application in Drupal, there are countless modules out there to help you with. Even if there is not as per your requirement, there are Drupal hook's to help you with altering your site as per your needs.
Drupal is more of a CMF (Content Management Framework), in which you can develop anything you want from normal website CMS (Content Management System) to ERP (Enterprise Resource Planning) to E-Commerce website, Drupal is everywhere and can fit anywhere in your requirements. You can even scale drupal with other technologies like MongoDB, Core PHP or anyother technology where drupal has a limitation.