We don't know when exactly, but we do want to deprecate the Windows-based vCenter. In 6.0, the VCSA has feature and scale parity with Windows. The only exception is that VUM still requires  Windows. However, in 6.5, the VCSA has surpassed Windows in features and performance while VUM has been integrated into the appliance. I would not invest any more time in the Windows-installabel. The appliance model is the future.