If we are to assume that Ethereum will become more popular as time progresses, and if we also assume - for the sake of argument - that the value of Ether will therefore also rise as demand increases, we might therefore think it likely that people mining in these early days might stockpile any Ether they mine to sell at a later date.
No, that would be a nonsensical assumption. Yes, everyone who holds one ETH has the right to the future appreciation of that ETH. But they can also sell that right for its fair market value. There is no particular reason you would prefer to hold it rather than sell it because you get the same value either way.
Every argument you can use to say that a person would rather hold ETH than trade it works equally well the other way around. The more people want to hold Ether, the more people will be willing to give to get it. Why do people most like to pay with dollars in America? Because that's what sellers most want. You can try to pay in other things, but they prefer dollars, and because of that, they make the best deals for customers who pay with them.
The more the seller wants what you have, the better for you. So every argument that I don't want to trade ETH because I want to hold it is equally well an argument that I do want to trade ETH because I can get fully compensated for selling that right.
The upshot of this is that the assumption is nonsensical. It is essentially impossible for there to be an asset that we all know will significantly appreciate. Why? Because if we all knew gold would sell for $35,000 per ounce next year, nobody would sell it for much less than that right now.