It's a neat idea, but could be implemented entirely in software with a RTLSDR. Not my cup of tea, but I'm all for absolutely ANYTHING that gets more activity on V/UHF.
A longer term project goal for me would be a SBC and a couple RTLSDRs with a good antenna that simultaneously does APRS igating, streaming audio of all the local repeaters and a few simplex channels, and notifications like this project, and like the "adventure radio" project that uses CTCSS tones to trigger alerts. I think it would be a nice service to provide for locals. The only "trick" is that RTLSDRs can only simultaneously decode within a 2.5mhz window, so it would probably require a little scanning to cover everything, or too many sticks. Doing a project cheaply, but effectively, encourages copy-cats.
This article shows a way of doing what I believe you are talking about, at least in terms of expanding RTL-SDR bandwidth. I have a couple myself that are collecting dust. Another line-item to add to the ever-expanding list of radio projects I want to try out.