I've been browsing some of these NHTSA petitions that are based on the substantial similarity argument. What I've learned from reading the denied petitions is that, having a good RI is crucial. Honestly, it's probably money well-spent to have a lawyer assist in drafting the petition and advising on the process too. For example,
check out this denial where the RI tried to import a Chevy Cheyenne pickup that was produced for the Mexican market. Seems like it'd be slam dunk for the RI as these trucks are pretty much the Mexican version of the Chevy Silverado sold here, but the petition was denied. Looking at the NHTSA denial statement, it seems like a lot, if not all, of their objections could have been avoided if the RI had done a better job.
Another thing I've noticed in the handful of denial decisions I read, is that, in each one, NHTSA reached out to the vehicle manufacturer for their opinion, and in each case, the manufacturer said the vehicles were not substantially similar. Which makes sense, why would they go out on a limb, they have nothing to gain. I'd expect NHTSA to reach out to Toyota if someone tries this, and my gut feeling is that Toyota will not be supportive.
Also, food for thought, check out
this application from an RI in Maryland. In 2012, this RI petitioned NHTSA to have IFS 100 Series Land Cruisers from other markets deemed substantially similar.
It was approved. The petition listed out the things that would have to be changed.
Another interesting one, is
this very old (year 2000) petition denial for 1989-1991 VW Golf sedans. In this one, VW chimed in and said that the European versions are heavier, have a different four wheel drive configuration, and approximately 100mm of additional ground clearance, and therefore would require crash testing.
Anyway, I like doing legal research. That was fun.