I'm starting to work with hardware and software for the updated V1s. Currently the most recent (with checksum), but I already have the alert scan. You can find two PDFs on Valentine1.com describing both the hardware and the software.
For the V1s that support ESP, any 5V safe TTL UART will read the data stream, so you can just feed it into a bluetooth module or serial interface to see what is happening.
Sending data is more complex and involves timing, but I'm working on doing all of that in a microcontroller. Send a valid message and it will go out according to spec.
In my case I'm using an ATtiny4313, using the ICP1 to read the UART data. I can already ask it to send the scan data. I'll be continuing and tweaking but I thought some might be interested. I'm also working on circuit boards so it would just be a plug-in accessory.
I want to connect it via bluetooth, so you can use almost any Android device or computer (or jailbroken iOS if someone wants to bother) to send and receive info. They bytes are easy to generate, but sending them out correctly according to spec requires some fancy timing.
Things will be posted to my github site (and I will probably add articles to harleyhacking.blogspot.com - I also have a new 20HzGPS/J1850 going).