Pokemon Sky and Earth version now both of you be quiet

i liek that... but what would the third one be?

Sky and Earth is cool, but a bit of a departure from their current naming.

Personally, I think Pokemon Opal and Jade would be good, with Titanium as the third.

I don't think anyone cares about rarity, but Nintendo do care how nice the names sound. Amethyst? Tungsten? No, I don't think so.

Just thinking about it, i'll take a bet with someone that the next versions are Opal and Jade. It's a big shout mind, so I'd need a big incentive.

They probably already have the name chosen and half the pokemon made.
They probably picked them because they expressed the tiniest bit of intrest in those names.

Tyranitar = Blaziken = Salamence > All

I want more Dragon and Steel types in the next gen!!!

The other thing about pokemon titles is that they emphasized parts of the game.
gold and silver (gen 2) introduced the Steel type
ruby emerald and sapphire introduced drastic improvements to the series with like 80 new moves and some hundred new pokemon.
gen 4's pearl diamond platinum, one of the main things introduced was the pokeradar which enhanced shiny pokemon hunting.

So, while they all do seem to be more valuable than the next, they also have specific reasons for their names.

Because there is just about nothing rarer than the last three titles, except for radioactive material, I would think they would go something to do with moon earth and sky like xxain wrote above.

However, those three mentioned in the OP are all shiny, all have various colors (ie topaz can be almost any color) and are pastel colors in their normal form.
This could mean that shinies will be back, and perhaps with new variations (multiple shiny types), and will probably introduce new types.

I believe they will just call the next game Pokemon 2 and go through all the versions again with some enhancements.

hmmm i have a couple of shiney pokemon.it almost cost me my life

Most of the shiny pokemon were not hard to get by the end of the game.
I figured out how to get any tall grass pokemon as a shiny.

However, once I had probably one of the rarest pokemon. It was that christmas tree looking pokemon that you get from smearing honey on the tree. I later traded it for what I found out was a hacked shiny pokemon. What a waste....

seriously could have sold it for like 40$ or something.