Regarding Realmshaper Engine and Vortex
You can and should garrison Slann on Vortex in RE. Vortex's rule "As long ... on the battlefield" clearly means only for it to be treated as one with model on it. So if it treated as one model, then you can put Slann on a Vortex, teleport him near RE, and in next movement phase put into the garrison.
And if you need to save your Slann you can take him out of the garrison (this uses his movement in this phase, right?) and then instantly teleport him away from danger. As LoSaT now happens in the end of the movement phase and is
not considered this unit's move.
My point is, if they don't specify any information about garrison and any limitations, then you can:
1) Set Engine on the battlefield wholly within your territory
2) Put inside Slann and Skink Starpriest
3) Summon Vortex and Cogs (as rules states - model in garrison can attack, be attacked, cast/unbind and use abilities; anything but move)
4) Enjoy your Slann with 2+ rerolling save, -1 to hit, summoning stuff atop Pyramid
We need to see full warscroll, but as I see it now - this thing is awesome and has a great potential. I will definitely buy one.