Sorry, but there is no use in making it open source... This has been said before, but HS 1.x was built using AS3, Flash, and several third-party non-open source plugins. Even if we were to release the source for HS, the third-party plugins necessary are no longer available. Without these plugins being available, it would require a complete re-write of the whole HS engine... that would take as long, or even longer, than continuing with HS2. We, and the dev team, couldn't do anything with HS1 code even if we really wanted to.
Instead of fighting and trying to work around old coding and tech, HS2 is the way to go. Anyone is more than welcome to keep using HS 1.5 until they are willing to switch to HS 2.