HODL/Investment = Profit
at some point spending will begin...
Whenever they want to. How are we supposed to decide when someone is going to start spending their money? They can hold until they think that they have made enough off of their holding, and then they can choose to start spending. It all comes down to the individual's desire to hold, and nothing more than that, really. You cannot decide what someone wants for them, it is entirely up to them to choose when they have enough money stored up and they have the desire to spend money on something.
If they never have the desire to spend, so be it.
It will depend on the hodlers, If they are hodling the coin just for the future then there is a low chance for them to sell it. What they are waiting is for the coin to be priced thousands of dollars before releasing the coin. For people who just have coins and used it for daily expenses then expect them to spend the coin every time.