Do you know how expensive that would be?!? Clubs don't make profit, and 30 race fees aren't going to cover all the running costs plus employing marshals!
At our local track, none of the marshal points are in dangerous places, and if there are any that could come 'under attack', they have 7 foot high fences around the marshal point to prevent that kind of issue.
I can see them taking away the main jump section (you can easily cut it off due to the track design, and still have 40 second laps) if there is an electric class though, as I have almost got outside the track area before - which is dangerous.
It's fair enough that a nitro driver blips the throttle or revs to let the marshal know that they are there, and to keep their engine running (unfortunately

), but not when a marshal is next to them - all sorts of stuff could end up in their eyes/face. This was particularly unpleasant at our track's old location, where sheep would jump over the fence and crap all over the track...