Well let the truths that we already know of about the Sacrifice stone heres what we know.
There is a Jetpack Drawing on it.
Trevor can sacrifice random people by giving/taking them to the Altruist Camp.
You can kill Altruist on the Stone once in the camp fighting them.
My Theory is could an Astroid Impact the Stone to reveal the Secret Inside the stone?
Is there a possible cutscene involving the stone?
What if we go to The sacrifice stone during a Full Moon or any of those found on Glyphs?
Let the Theories and Test commence.