That would have required exactly as much work to transition, plus require computers to get good at 48-bit math. ("Why are the top 2 bytes always 0xFF?" "I don't know, grandson, but I'm sure it seemed like a great idea before Y248.")
No, it wouldn't have taken 'exactly as much work to transition'. See another reply. In 2024, I'm still reading about BGP/routing table issues, and hardware having problems keeping up with IPv6 networking - it's just too large. How was this supposed to work in 1999?
A smaller stepped transition from 4 billion addresses to... 64k of those would have been an easier transition step, and the ease - mental, UI, training, testing, security, etc would have given everyone involved the confidence and positive feedback to tackle a next stage to IPv6 (eventually).