I can mention that I have offered to buy geocheck.org at a point. There was obviously no deal made.
Implementing a new geocheck-site is not of interest, I think there are way to many already, it would be the best if only one existed in my opionion. Also, creating a new would be months of work, and then probably 1-2 years before there was a good user base, even with Project-GC backing it.
Project-GC has a lot of things on its TODO-ilst, about 1-2 years of full time work still. Adding a geocheck project to that right now isn't the smartest move. There are good sites out there, we rather spend time on implementing what others don't have.
I agree that it would be nice to have everything at one place, and that is also why I looked in to it 1-2 years ago. But I do not believe it's a good strategic choice. Neither for Project-GC or its users.
And to make it clear. There is no official relationship between Project-GC and Geocheck.org today. We just host the site on our servers. That whole thing started with that geocheck.org's provider just shut it of without prior notice. It was a bit of an emergency in the geocaching world and I acted. As a thank you I got quite a lot of referral traffic to my new site (Project-GC).
Besides the hosting by us, and the link to Project-GC at Geocheck.org, there is no cooperation between the sites. Or well, I have made a lot of patches in Geocheck.org, both for security and for performance. And I have also dedicated a mystery cache series in honor of Geocheck.org. It is a bit special, if you want to look at it, focus on the one with low D-rating first. Not #1 in the series.