Microsoft abitrarily taxes VDI
One potential barrier is the cost of VDI. You see, Microsoft was forced to create an arbitrary tax on VDI through a new annual renewable license called the VDA. For every NON-Microsoft client that is doing remote desktop to a Windows host, you must purchase a VDA. The only way to avoid the tax is to use an all Microsoft approved infrastructure for VDI. I hear that EA users can exchange their unused CALs (which are "one time" fees) for an annual renewable VDA.
Basically what Microsoft has done is greatly raise the TCO of a typical VDI deployment. But of course, Microsoft will gladly "make a deal" with you with regard to the "tax"... so it may only be a tax against SMBs. We'll see.
The VDA is an anti-competitive practice btw. As it coerces companies to choose only Microsoft approved solutions.