My experiment was a success! The seeds are viable and the first one germinated today, 5 days after sowing. Pretty much all cactus seedlings look like this when they first germinate, so it’s still way too early to tell if they’re a hybrid of my Astrophytum coahuilense and ornatum. It will probably be at least 4-5 months, maybe even a year before you can properly spot the difference between these hybrids and “purebred” ornatum or coahuilense.
First, let’s just see if they actually survive the tiny seedling stage.