The spring-summer timeframe is the biggest issue to deal with here. I think that this design would have to have a sacrificial layer with decomposing, anoxic material which degrades during the warmer months. Perhaps it could be mitigated with various expedients to decrease the ambient temperature like flooding the surrounding landscape or putting a shade over the pile.

This scheme only makes sense if the amount of biomass added every year is much larger than the amount which is present in this external layer.

Anecdotally, my father has told me about soaked hay bales out in the pasture which still had a frozen interior core by late May.