You said, "Make it flexible, and agree to reassess as you go. "
Then you said, "This partially explains why I believe the "slicing pie" model doesn't work for many different companies as well"
Um, are you sure you understand the Slicing Pie model?
Slicing Pie is the world's most flexible equity model that gives teams an automated way of reassessing the split over time and specifically takes into account this thing you also said: "Everyone on our team has a full time job, a spouse, numerous children. We aren't going to make a dime off this for at minimum 1 1/2 years, maybe more. I'm asking these people to put in time after a 45+ hour week, without pay, to work on our project at midnight on a Tuesday."
What you described is the exact reason that Slicing Pie works so well! I'm not sure I can even come up with a more perfect case for Slicing Pie.
I'd be happy to share a copy of my new book!