Some things done to "tuner cars" are indeed conceivably unsafe (Having no functional suspension, having excessive camber, having screwed up steering geometry, etc) but the number of those cars on the road has got to be 0.1% or less. I've seen the outcome of a case where a VW Jetta with excessive camber evidently had the connection between the knuckle and the strut break. Those cars are not designed for that connection to be adjustable and it has to be modified (a.k.a. weakened) in order to allow it. But a customer of mine had a bone stock Honda Civic have the front suspension collapse because of a broken ball joint, so it isn't just modified cars that can have stuff break. Fortunately that one happened at low speed.
The bigger problem for the average person is that the new procedure takes around 3 hours of labour to do properly ($$$) and normal wear and tear will result in a "fail" even though the situation is not really unsafe. Basically it means any car will be more or less worthless after 3 years because of the excessive cost of having the inspection done and of replacing all the suspension and steering parts that have rubber bushings or boots.
I know my own car (which is a 2008 with 230,000 km on it) would fail:
- Aftermarket HID headlamps (in projector housings ... the beam pattern and low beam cutoff are good ... The new standard doesn't recognize that aftermarket lighting might actually be good)
- Aftermarket muffler (flex pipe broke on the original - the replacement is just a smidge louder ... but it's not OEM ... definitely not obnoxious. Broken flex pipes are a common occurrence on this model ... the aftermarket is warrantied for life and has already been replaced once, the dealer will tell you to pound sand and make you pay for the replacement)
- Non-stock ride height - Complete Bilstein kit designed for the vehicle and professionally installed ... and with appropriate bump travel in reserve ... but it's not OEM parts. The interesting bit is that Bilstein is the OEM suspension supplier but the OEM parts are built to a price (no adjustments, cheap valving) and the aftermarket bits have the proper valving and adjustable ride height.
- Non-stock tire and rim sizes. The tires come within 1" of the fenders when turning ... but they don't hit. Not a safety hazard ... but it's a fail. I think the STOCK tires come within 1" of the fenders when turning, but the only way to prove that is to put the stock tire sizes back on. (fortunately, that's just a matter of swapping to the winter rims). The rims on the car are actually OEM rims, just not for the trim level that mine is.
- Worn front swaybar bushings. This one I will grant as a legit reason for failure although it hardly makes the car unsafe to drive ... it just makes noise over bumps.
- It will probably need new front lower control arms ... that's the only way to get new ball joints and bushings since it all comes as one assembly.
The average cop looking at my car wouldn't know it ain't stock.
I don't own a vehicle which is not modified.