I think ignoring it completely is a viable strategy once you've already gone through the stages - when your mind is in the right place.

I have moved on a long way from the days that 12 factor was my bible, but those days completely redefined my way of developing software. I'm not exaggerating here - it completely shifted my approach.

I guess it's similar to Scrum in that way - it isn't a great end point, but if you're stuck in the old ways (i.e. the methods used before it was even a thing) then it's at least a good approach to sink your teeth into, try it out, shape your approach, and move on from there.

Basically, I'd rather see a replacement that improves on 12 factor than throwing out the book entirely.