Technically Gold does generate cash flows. It provides the real return of money. It's not a cash flow that flows into your bank account each month but those cash flows are embedded in the price of gold and it's one reasons it appreciates or depreciates across time.
Volatility cannot go to zero but XIV certainly can and no doubt will at some point in the future. XIV is nothing more then a complicated swap. It's aim is to replicate the behavior of another derivative. People can call anything whatever they want to.
That can be stated of anything that trades (gold having cash flows). That's what defines a tangible asset. You can't define gold as an asset that provides a return; only that it's convertible, having some innate value related to it's physical properties. There is also an opportunity cost with holding gold (-CF).
In that sense a varswap (and more so, gamma swap(embedded floor)) can be considered an asset. It will always maintain a positive value.
We're really not talking about a leveraged ETF, even though it should always maintain some value (=cash).