Ok I’ve worked out what I think - speculation klaxon! - their original plan was, long before relations with the RF soured.
It’s dependent on them expecting full agreement for what they do, regardless of how realistic it is that HMQ would agree.
Marriage.
Phase 1: Live in the UK for a while. Separation from W&K in terms of charity.Do long holidays in North America.Set up the charitable foundation.
Phase 2: With the charitable foundation up and running and doing TV production work like the mental health doc, they set up a place in North America, possibly ‘temporarily’ and spend time there, months at a time. Depends on tax regulations and how they could avoid being double-taxed. But they don’t have a declared 6 months uk, 6 months US policy, it is all phased and not fully commented on to try and slip it under the net to a certain extent.
Phase 3: Archie starts primary/elementary school - in the US. For privacy, to be near M’s roots, and because their charitable foundation and TV work is doing well and an L.A. base makes sense. Harry and less so Meghan still come back to the UK a lot for engagements, for their patronages. They are doing the plum engagements, less so the dreary. They & Archie are at all or at least most major RF occasions. In this phase they do announce at some point that they are becoming self-funded to a certain extent.
Phase 4: Secondary/high school: Archie goes to boarding school in the UK. Possibly Eton. To give him an international stellar education and to honour his British roots. Harry & Meghan have two homes at this point, one in the UK and one in the US.