If someone has access to an IDX (or similar) file with all 50 states, I can certainly modify the application to do that. However, as I mentioned previously, I tested this concept out originally with all of the listings in the state of Florida and the count was around 120,000. The application performance was acceptable but I can imagine it slowing down if you multiple that number by 50. As long as the user makes some selections, the application should perform acceptably with any number of listings. It's when they just click "search" without filtering down at all and the application would have to pull back millions of records that would cause it to run seriously slowly... I could put some code in the application to force the user to filter down further when the result set is over a certain number of records. That would be fairly simple.
Anyway, the short answer is "yes" I plan on expanding this to include all states but I need to work with people who have access to the data. I'm not a realtor... so I need to work with realtors/brokers

to make this a nationwide product. Either that or I bite the bullet and buy my own access to the data (which I don't believe is cheap).