Am I required to update my existing Vive-compatible VIVEPORT build with Oculus Rift support to continue being distributed on VIVEPORT?

Absolutely not! We will only require you to have support for Oculus hardware if you opt-in to this specific feature. Our intention with this update is to provide publishers an additional distribution mechanism to reach Oculus hardware owners – we have zero intention of making Oculus support a hard requirement to publish VIVE content on the platform.