Positively charged gases
You totally can't have a gas (or any other state of matter) made of positive ions alone.

That's not what you asked, though. The question was: what if we theoretically could have it. Well, then in a pretty short instant you will stop having it. The said instant would be rather violent, too(*).

To put things into perspective, imagine an indestructible spherical vessel about as big as to contain 1 mole of gas at normal conditions, which implies the radius of 17.5 cm. Now let's magically put 1 mole of $\ce{O+}$ inside. That would give it an electric charge of about 96500 coulombs, which is quite a lot. The electric field outside the sphere would be $$|\vec E\,|={1\over4\pi\varepsilon_0}\cdot{q\over r^2}=2.836\cdot10^{16}\;\rm V/m$$

Do you know how big is this? Wrong! it is bigger than you think. Mere $3\cdot10^6\;\rm V/m$ would cause a breakdown in dry air. Good solid insulators can handle more, but I think we may safely assume that $10^{10}$ is enough to break anything that is made of atoms. Mind you, we have six orders of magnitude on top of that(†). The conductor will be instantly vaporized and thrown out with immense force, enough to start many nuclear reactions and create a bunch of weird elementary particles. What metal it was made of would be the least of your concerns.

So it goes.



(*) Reminds me of a certain what-if episode, but they used a bigger sphere.
(†) Thought we would break the Schwinger limit, but we didn't.