Not about hempcrete specifically, but I can see how you could potentially make a material like this. All these materials used in construction we can assume have an environment with a range of variables they operate in. If this material will never be exposed to high temperatures for example while in a typical operating environment... then maybe you can design the material to be able to biodegrade when heat is applied?

Just think about how even typical composting works where the point is to keep temperatures of the compost pile going in order to aid the process of breaking the material down in an acceptable timeframe.