With the announcement that the Windows version of vCenter will be discontinued, VMware will now release monthly Security for the vCenter Server Appliance 6.5 (vCSA) Photon OS.
See the official aaniuncement here: https://blogs.vmware.com/vsphere/2017/09/monthly-security-patch-program-vcenter-server-appliance-vcsa.html
The first one was released for 2 days ago.
Here is a link to the documentation for vCSA Photon OS security patches: https://docs.vmware.com/en/VMware-vSphere/6.5/rn/vcenter-server-appliance-photonos-security-patches.html
I think it would be great if VMware also included updates for the HTML5 client with this montly security patches. Maybe as an optional extra, this will get the new features out to the administrators much faster, and I think VMware will get much more feedback this way on the HTML5 client.
I Know that you can use the Fling, but it's not everyone that is using it, just because it has another DNS name, and that may be confusing. I personally uses the Fling, i our lab, and at a few customers, and give feedback on/from this.