While I do agree that some of the most recent MINI™ models do look like small SUVs -- I drive a small SUV and when a MINI™ drives past I think "Look at the size of that!" -- I think that Stephenson's own design was much too big as well. For me, part of the spirit of the original Mini was that it was tiny compared to contemporary cars.
And it's certainly possible to get a tiny car safety-certified today. BMW just chose not to.