I'm not sure I understand what you're asking, weapon slots? I know of my trusty two action bars, occasionally three when I use that Overloard ultimate but yes -, you mean a third action bar? Or the Q slot thing?
@Woolenthreads I distinctly remembering them saying that the tablets can be bought and sold and are also, in similiar to function to rune-stones, consumed upon use. Which naturally means, an aoe flame atronach spells, an ultimate flame atronach spell, a single target flame atronach spell, will be able to be placed on one action bar, as they're all different abilities. I remember this vividly as yes, my plans on having a battalion of serpents shall soon come to fruition.
We can have a clanfear, winged twilight and as many atronachs out at one time as we can muster, so I can't see why this would be different, providing of course, the abilities are all different so that they can be placed on our action bars respectively. As how clanfear, twilight and atronach function now.