Thanks for the extra details about your question & scenario.
While in DPS Classic subscription product IDs and Direct Entitlement Integrator IDs were baked into the app binary - this is no longer the case in the new DPS 2015. We have moved these items to be server-side as you've seen in the DPS portal Project Settings and Products & Subscriptions areas.
You can build & submit your app with in-app purchases. Later, when you want to enable Direct Entitlement, you can enable the capability and enter the necessary data (Integrator ID, Bundle ID, Create Account URL and Forgot Password URL) in the DPS Portal, Project Settings > Direct Entitlement (tab).
You do not need to rebuild your app or resubmit to enable Direct Entitlement.
I ask this question as it seems separate in the Web UI from the application portal in the Web UI. It DPS Classic, the entailment options were added during the App Build process in the App Builder. Can I submit a non-entilment viewer now, and later change the setting in Project Settings, or should I upload the original binary with the entailment features checked now even though my content will be iTunes in-app purchases for now. Or will I need to upload a new binary later with entailment options and go through Apple Review again?