Hey,
I see your point, I have used a bunch of beta and experimental plugins before, the only difference here is that substrate is a complete overhaul of the material system. If we wanted to suddenly revert back to the “vanilla” system, It would be a nightmare.
On the other hand, the look of the show I am working on is very specific and will probably require more flexibility and quality in the shading which Substrate provides.
If the only downside is risk of support being cut off then I think it is risk free as I highly doubt Epic will abandon this system, it is likely to completely replace the vanilla system.
Thanks for your input!