Dunno... The way I see it, a hacked safe is no different than glitching/duping in terms of cars. If we can deal with that without GT breaking down, it should be the same for hacked savegames.
And personally, I don't care about trophies. Neither my on, nor those others have, Especally not those of others.
And since you can't dupe skill or experience with a given car, I don't even consider havin all cars available as a big advantage. Inf act, i think that those who focus on a fistful of cars will be usually at an advantage as they are mroe likely to wring out more potential out of their cars.
So, as long as a car's statistics can't be altered to turn this into genuine cheating online, I think it's not that big of a deal and not too far away from what we're seeing now, anyways. It'll just be done in even less time.
I still don't like it, but what can you do... Sure, it sucks royally if you do care about comparing trophies or whatever, but aside from that... As long as they can't mess with you on the track, it's not that bad.
I wouldn't be suprised if they can, though. Banning cheaters from PSN manually might work, though. But... If a PS3 has been 'jailbroken', can they even stop a cheater from settign up a bazillion of PSN accounts?
Either way, I don't like hacking, glitching, cheating, duping, whatever you wanna call it and I can't really get where the fun is in that, but that's just me.
As long as nobody messes with my 'Ring while I'm hotlapping, I'll be good, I guess.