Based on that list, nobody will be using the hot add CPU feature then!! I remember when this first came out a colleague said “Windows would through a fit if you threw another CPU in while it was still running” and the list suggests they were right.

I liked Scott Lowe's approach in his vsphere book. He has an application owner demanding 16GB, so he assigns the box 16GB and then puts a limit on it of 2GB. App owner is happy as he thinks he has 16GB and VM admin is happy as he has only given out 2GB. If it needs to be amended on the fly, well you just increase the limit, sort of like hot adding memory. Suppose you could do the same with vCPU's and number of clock cycles. Although this approach takes a little more thought and management if the server is important enought to need Hot Add then this approach would give you that zero downtime capability on OS's that are not supported currently.