I've never heard of a parent being concerned about console mods, of all things, and I (as a parent) don't really buy this angle. The original Xbox's weak parental controls could be bypassed by pressing X Y Left Trigger X, a tidbit that was quickly distributed throughout my middle school to let everyone launch M-rated Halo discs. Presumably if publishers were actually pressuring Microsoft to make a child-safe device, they'd have come up with a more advanced protection mechanism than that.

Modifiability/vulnerability would not affect my game console buying decision as a parent at all, provided the console had some form of cursory parental controls. I'd probably choose a console that didn't have such a simple bypass as the original Xbox, placed head to head with another console, but if my kid has to go online (!), learn about exploit development, and run some advanced tool to bypass parental controls, that's a valuable learning experience, and they were already on the Internet somehow, a much more dangerous place than an M-rated game anyway.

DRM and cheating are the drivers for game console secure boot. Cheating is getting even more important than DRM, really, IMO - it's one of the places where consoles have a huge edge over PC gaming.