VMware has announced through vSphere official blog that #C client (also known as AKA Desktop Client/thick client/vSphere Client for Windows) won't be available for the next vSphere version.
Current VMware hypervisor versions (6.0, 5.5) will follow the standard support period, so they won't be affected.
The company is going to replace this desktop client for vSphere HTML5 Web Client, which they ensure is "faster and improves user experience".
VMware has been working towards HTML5 transition, which have become the official interfaces for their respective components. This is the case of Platform Services Controller UI, vCenter Server Appliance Management UI and Host Client. The last one to change its management interface was vCenter Server. Now it's vSphere Client for Windows's turn.
For further information on the new client and how to perform transition have a look at VMware vSphere blog