I just watched that, as it popped up on my YouTube feed, came here to talk about it, and there it was already mentioned by you!
The 18 month thing sounds absolutely catastrophic. From my experience of working on large software projects, someone who has been employed for 18 months is like a baby just learning to walk. The real work is all done by people who have been there for an absolute minimum of 2 years, and for the really serious stuff, it's done by people who have worked there for 5 years plus. Senior managers see software developers as being as interchangeable as typists and have absolutely no grasp of what it takes to understand hundreds of thousands of lines of code and architect new areas of development to fit in with that massive existing code base. Even if FM was built from the ground up by new starters, removing the problem of needing to architect it to fit in with existing code, you'd still be throwing away all the expertise gained from development of what existed before. The real value in starting again is you create a new architecture that fixes all the problems the old architecture had, but that requires the work to be done by people with extensive experience of the old code base.