VMware has finally pulled the plug on the C# client, or at least in the next version they will. Going forward everything is done via the web client, which has been improved significantly over the last couple of years.
Reading more here there’s more background on this and I have to say it’s a long time coming.
So already I’ve heard the grumbling of having to use the web client but with VCSA 6 I have already seen some nice improvements and to be honest I live in PowerCLI for the majority of my tasks. The second link referenced the pure HTML5 Client Fling that seems to be the basis for the new vSphere Client so I would say reserve judgement until you’ve had a chance to check out the new client.