The other potentially very damaging story I've been waiting to see hit the media is the final verdict on his very dubious involvement with Jennifer Arcuri during his stint as London Mayor.
Surprise surprise, she has since confirmed that they were having an affair during the time her company was awarded financial and other perks by Johnson's office, despite his claim to the contrary.
If that surfaces soon with at the very least a stiff reprimand then I can see more of his support chucking in the towel.