There is Soul Stealer Vayne on the way to Hextech Crafting, so hopefully as time passes we will see more 10 gemstone skins.
Hextech crafting was obviously meant to rack in more cash, yes, but it still is supposed to be and function as a free system as well. Getting and earning chests and keys through games over time, slowly getting gemstones, seems now to be a wiser idea then spending cash if Riot is releasing more 10 gemstone skins. It's like a way of saving up for whenever a skin you like finally comes out.
Now, mind you though, I am just speaking hypothetically.
This is Rito we're talking about, so Soul Stealer Vayne might be the last one we see, or 50 more will be released in the next few months and Youtube will become cluttered with Hextech Crafting opening videos.
I feel safe betting we'll see more 10 gemstone skins as time goes on.