I came across below video which is a wedding photobook made entirely from video frame grabs, the album is quite basic in layout but looks like something you can sell as a add-on which would not require much extra work the day of the wedding. Not sure if a 4K camera was used but when doing this the extra resolution would certainly be a benefit.

vimeo.com/123148908

Until I saw that video, I wasn't sure on how good frame grabs could really look. As you say a good add on to my video service and a way to dip into Photo without actually offering it as a full on side service. I may offer it as a freebie for my top package couples, then add it as a paid option once I've got samples to show.

I never had any ambition in doing video and photo at the same time but if I was able to shoot video like I always do and afterwards in post just extract stills, then I wouldn't mind. It never would be of the same quality compared to a experienced dedicated photographer but if the couple would understand and agree with what they will be getting it might be a way to charge a nice extra amount on top of my fixed videoprice just to do the work afterwards in post. I have noticed that 4K frame grabs from my gh4 grade very nicely in lightroom.