It will show the icon of whichever talent you have active and it will cast it too.
I have a macro like this for Living bomb and Nether tempest and it works just fine.
Thats because blizzard made living bomb, nether tempest and frost bomb to be interchangeable on one spell id called Mage Bomb. mop.wowhead. com/spell=125430/mage-bomb(Cant post links yet, so remove the space). That will show in your spellbook if you haven't chosen any talents in that tier. So it wont work on any other talents, Unfortunately. I would actually love if blizzard implemented this for every talent tier. Or just made a quick fix for macro's, so the tooltip wont show unknown abilities.