I noticed the following note in the developer guide article.
This note embodies a big promise for many organizations that are currently planning or actually migrating from version 2011 (and up) to version Dynamics 365, as it removes (or at least dramatically postpones) a big chunk of work required to migrate code that uses the 2011 SOAP endpoint to use Web API endpoint. In typical enterprise level projects (versions 2011 to Dynamics 365) the 2011 SOAP Endpoint (a.k.a OrganizationService) is heavily used in Plug-ins, Custom Workflow Activity components, external application integration and even client side code.
For organization planning an application re-do (rather than an upgrade) this means an option to re-use existing code investments (e.g. non-changing integration points with external applications).
When considering an upgrade to Microsoft Dynamics 365, code components migration is a primary workload for most organizations. Although it is recommended to use the modern Web API, reducing or eliminating this workload means a whole different time frames and resources requirements for the migration process.