I agree with a lot of this. I don't like that Morrison made "our Earth" part of the Orrery, because it doesn't make much sense for the real world to be among DC's fictional ones.
It should sit outside all known structures, generating DC's entire Multiverse, not just the Elseworlds. Everything is literally a product of Prime Earth.
Regarding Earth-1985, Earth-2 and the Doomsday Clock Earths, my head canon is the following:
Each major continuity reboot created a new Multiverse to preserve the former Multiverse's history.
So there would actually be a bigger structure, an Omniverse that would be home to multiple clusters of Earths:
PRE-CRISIS MULTIVERSE
Original Earth-1, 2, 3, 4, S, X and so on.
POST-CRISIS EARTH
Not an actual Multiverse. Like in the original Post-Crisis Earth, this Universe would be the result of the merger of all previous Earths. It would be apart from all other universes, its Earth essentially being the last Earth known to its inhabitants.
NEW 52 MULTIVERSE
Home to Earth-52, Earth-53 (its Earth-3), Earth-54 (its Earth-2) and all Earths closely derived from the New 52.
The METAVERSE would be the Multiverse that's constantly in flux, responsible for the creation of these mirror Multiverses.
Every time a new reboot happens, most of the Earths gravitate toward the new version of the Metaverse. So essentially the "main" multiverse would look a lot like the Multiverse shown in Morrison's Multiversity, except its Earth-0, Earth-2 and Earth-3 would have relocated to their own Multiverse, being replaced by the main Earth and new (more classic) versions of Earth-2 and Earth-3.
I also think the Earth-1 from the OGNs line should be apart from all other Multiverses. I'd rename it something like Earth-α. Since it isn't a fully formed universe yet, it would be set apart from all other Earths like Post-Crisis.
This way the main DCU Earth could be called Earth-1 again and the OGNs would still have a clear brand (DC Alpha, like DC's version of the Ultimate line).