It's a nice thought but I think it would be hard to make it profitable. The internet-only dealers have low overheads and could undercut a dealer who has a showroom to drive them out of business, unless that showroom dealer has a strong established reputation (e.g. Jurgen). Good for driving costs down (temporarily at least), but bad for the dealer who is sacrificed in this way.
Like others said, yout couldn't really specialise in supras: target market not big enough IMO. You'd get plenty of pats on the back from people on here, but that doesn't pay the mortgage.