The multi-image approach in NCS will not make it's way into mainline Zephyr because
Is there some record of the rationale behind this? (eg PR #).
I'm wondering that if its rejected from mainline zephyr for reasons like 'out of scope' etc then maybe there is some existing consensus for alternative ways - or if it was due to lack of demand then maybe that can be reappraised... But that's a lot of "maybes" and "wonderings".