I didn't see that. Wow, that's a huge gap. A quarter round or shoe molding would do the trick, but it's going to have a large vertical profile that may look odd. If the end closest to the camera leads to an inside corner, they could buy matching trim for transitioning different floor types. As long as you had some scrap wood to put underneath, should be solid and not look so out of place.

I think ripping up boards may be the best option. Sucks, but better than having a poorly finished product for years.

It looks like there is already quarter round installed. If I'm seeing it right, I don't think that is going to be an option. Most want a 1/4 inch, not 1/2 inch, but I'm sure that varies by material.