Many customers thus far have opted for greenfield implementations, deploying "clean" S/4HANA 1511 environments alongside existing ECC environments. Greenfield deployments provide some distinct advantages over conversion:
Your existing ECC environment stays in tact while you plan for a gradual (or abrupt) sunset.
You can control the roll-out of S/4 innovations and S/4 requirements like Fiori apps, Customer/Vendor Integration (CVI), and Financial Supply Chain Management (FSCM) to your user base, supporting adoption at a pace that works for your business.
You avoid a true production outage, as your legacy ECC and S/4 systems will run in parallel until you sunset ECC.
You can deploy S/4 without having to worry about managing SAP and third party add-ons.
You can rely on your existing ECC environment while waiting for S/4 to allow IDOC output management (forthcoming article) and other functionality that may not be in the current release of S/4.
On the other hand, there are also advantages to cutting the cord to ECC and going through an ECC conversion to S/4:
You avoid the cost and maintenance of running parallel ECC and S/4 environments.
You enable your business to quickly adopt the full range of S/4 innovations.
You establish S/4 as your sole platform for innovation, enabling you to plan your short-, mid-, and long-term roadmaps based on the S/4 platform.
There is no right or wrong path to S/4 -- both greenfield and ECC conversion are viable options. Your decision should center on how much innovation your organization is ready to take on and your ability to support organizational change management around this innovation.
Of course, there are other starting points in the path to S/4 aside from ECC 6.0 on AnyDB. In the first few years since HANA's introduction to the marketplace, many customers have completed an OS/DB migration of ECC from AnyOS/AnyDB to Linux/HANA. If you are running ECC on HANA (ECCoH) and are considering an S/4 conversion, the key changes you will face are the new code base and functional changes inherent to S/4. Or, if you are running ECCoH with Simple Finance (i.e., S/4HANA 1503), converting to 1511 or any release that entails the S/4 core will primarily impact your logistics business.