Very interesting idea...As I read this post it reminded me of my indoor gardening attempts in college...LOL but we won't go into that. I remember using rockwool cubes for clones and yes it did have great water handling properties.
Rockwool is an interesting idea and yes I think it is worth looking into if nothing else than just as another option for the breeding community to chose from. Please let us know how any test end up good or bad. It doesn't have to be a success to share, we all appreciate people willing to share their failures also. Everyone benifits from the knowledge either way.