I did say ROAR....
...And that their rules didn't directly apply to the UK.
However, as the US is one of, if not the, largest markets for RC, mass manufacturers are unlikely to develop a vehicle that does not meet the ROAR rules.
Obviously small niche manufacturers or pure hobbyists could create whatever concoctions they deem appropriate as long as they fit within their local rules (assuming they are racing at sanctioned events). AFAIK, the BRCA only has a max dimensions rule on Lipos, certainly for 1/10th OR.