Playable race? Definite NO!

Playable clan? not likely.

Garleans are not all that different than Hyur's in general. The only real difference being the fleshy orb on their foreheads. If they were to introduce Garlean as something playable it is more likely that you would play as a mix blood garlean and it would function as a third clan type. However this is also very unlikely. (which I do hope they go back and add new clan types for older races to expand on customization)