1) that has to be the worse case of premature optimization.
2) just solve the puzzle? The existing domain name system was wonderful when it was introduced.
I'll do a crude solution that shouldn't make it to the short list of goodness: Just make the commercial part into a web directory with all registered businesses. Have some of those filters we are now all familiar with. It might even smoothly transition into a product catalog. Sell placement rather than some random name no one will accidentally bump into. Let's also do a nice tag based web directory for personal websites. Extra points if there is opml
<link rel="outline" type="text/x-opml" href="webdir://hotel" title="Hotels">