I am assuming that a 1080p HDMI out signal on 5dm2 falls under features that are not possible...?
No , 1080p is possible you have to do a little post work thou depending on your HDMI capturing device .
First the 5d2 was never intended to do all thing it can do now so HDMI output was not really configure for Wide Screen 16x9 A.R.
rather it was more Square frame 3x2 A.R. so instead of 1920x1080 you get 1650x1080i60 (YCbCr 4:2:2 8Bit) with side bars but wait you say

that's 1080i not 1080p , yes As long as you are filming in ntsc @ 24p in the main system the HDMI will embed a 24p inside the 60i signal .
Depending on the capture device some will do on the fly
3:2 pulldown reverse telecine for the ones that don't like atomos ninja first version (I have one)
They record the 60i (interlaced) , I just load the files in apple compressor or adobe after effect and apply the reverse telecine switch and 3:2 pulldown are automatically performed .60i>23.976p
clean hdi out?
Yes , in the magic lantern menu under the display tab "Clear Overlays" submenu "Recording"
So when activated there will be No overlays at all period , including any raw video recording time when recording raw.
In Standby mode everything back to normal , overlays are visible again.