Agreed... now would be a good time to pull that deep.. you can use the drawn frames to replace any remaining frankenframes...
If you add a medium with un drawn foundation, pull up a couple three frames from the sides they are not using and out in the middle of the medium. Put the new frames ou move down to the outside edges of the brood area without breaking up the brood... They are obviously making new comb from the looks of the inner cover, time to make them busy!
Plastic will work fine. The only time it doesnt is if you give them a choice of wax AND plastic, then they will generally choose the wax and ignore the plastic.. with no choice they should start drawing right away.
Not sure why people want to see if they will "like" using mediums over deeps.. As far as I know, nothing about it is any different except the weight, Oh, and the ability to use drawn honey frames as brood frames in an emergency, Oh yeah, and there is better communication because of the extra gap, AND, you can save some of those super frames to put in the brood chamber to feed the bees next winter, ok, I'll stop