In my honest opinion, the only use I would get out of a OFW Garage Editor is to change the chassis of a car (tire width too if it's even remotely possible, maybe it's just a CFW thing like wheel swaps.) Because all I've been mostly doing since the release of Gran Turismo 6 is taking pictures and doing videos.
I understand that the main concern and frustration of other users that if a hybrid tool is released, they will abuse it to do ridiculous amount of horsepower for their cars, ruining the online experience for another user.
But with GT6, we've got the option to kick users out of a lobby and it could help in moderating some of the chaos. Personally I don't do much racing online, only with a friend of mine when I need to make a video, but I mostly do them in Single Player.
I know that some users would like to use the tools for good, creating replicas of cars and some real world engine swaps (Example a LS1 on a Mazda Rx-7 or RB26DETT on a Silvia S15) and I find that to be very interesting.
In the meantime, I'll just do the same thing I've been doing for a while now, lurking in the "Hybrid Picture Thread" and admiring some of the creations you guys post. Regardless if an OFW Garage Editor is released.