Like The Gamer Brewery said, I would love to see the ability to have summons that you can add (and maybe even place if possible) to the grid. The grid system would definitely be a lot fun to use with actor summons (not to mention that would add more flexibility and fun in creating a battle system!) especially since to my knowledge in-battle summons doesn't seem to be an actual feature in RPGMaker's normal battle system.
Also do like the idea of having the "back" actor being unable to be targeted until the actor in "front" is cleared first. I know you already mentioned something along the lines of this up above but it would be cool to have it so that if the two columns are like this:
Front-Back
G1 G2
G3 G4
G5 G6
G7 G8
Then if an actor is put in row G1 the actor in G2 can't be targeted until the G1 actor is killed. But if G3 has no actor then the enemy can straight away attack G4's actor. So, basically, if there is no other actor in the "front" column of the grid then the "back" column that is horizontally aligned with that column is targetable. If there's an actor in the "front" column, however, than the the "back" column is targetable.