I think it's a good idea. Certain maps are chosen by HB over and over again. Open-sourcing it could allow a community-maintained blocklist or voting system to reduce the appearance of maps that are crappy or just don't work properly. The random map picker could also be modified to not choose the same map more than once in the same session.
Also, maybe somebody could use the sourcecode to make a Project X hosting bot. Anything that can help bring PX to the masses would be very beneficial to WA's longevity, in my opinion. I'm sure there would be tons of benefits to open-sourcing HB that we can't fully predict right now. If nothing else it would reduce hosting costs on the centralized HB server.