I don't think they exist for .GDI since that format only really started being used for booting backups in the past decade really. As far as popularity of trainers go, they are at least still a thing on PC games, I know for a fact OG Xbox had literally thousands. I know 360 and PS3 had some too. PS3 has something called Apollo Save Tool which now can also download a lot of custom saves and game codes from the net directly from your PS3 since it was updated a year or so back. So Trainers are still popular. But maybe people would find it easier to load gameshark codes or game saves than coding trainers for each game? I would love to see them make a return though, a lot of awesome game hacks could be made with it.