As far as I can tell now, the reason why something like this doesn't currently exist is because of restrictions on access to MLS data. As of now, your only option to accessing MLS data is through all the individual local MLS', which as far as I can tell is restricted to realtors and to their clients through (frequently ******) MLS portals. The other option is accessing MLS data through third-party website like Zillow, redfin, or other small realtor web portals. The issue here is that data scrapping these websites in a dirty word in the real estate community, and essentially all of these sites have protections against data mining. So the limitations to the software appear to be primarily related to the restriction of access to data, rather than the lack of folks out there willing to develop the methods. It'd be really interesting to do nationwide data analyses of price:rent ratios and other screening factors to find outliers, but sounds like that's not in the cards.