@Bruce G the instancing barrier between ODY 4.0 and HOR 4.0 is a major letdown.
This is how I think it should be (no demand, just my personal opinion of what would be an elegant solution):
Horizons 4.0 should basically be Odyssey with some features restricted. Horizons players don't get to land on planets with tenuous atmospheres: Restrict them from buying the required planetary landing suite. Horizons players are not entitled to on foot content: Allow them to actually disembark in their flight suits, but disable any and all station concourse services. No pioneer supplies, no missions, no nothing. Allow full physical multicrew on ships and SRV. That is basically Odyssey with just a few but key features locked on a per account basis.
Horizons players could look at the station interiors but not use them, they could be taken down to a restricted planet on an Odyssey multicrew ship and could take gunner role in a Scorpion for Odyssey content. That way they'd actually get some use out of the Scorpion, but by far not the whole ODY picture.
Simple, elegant, and very little coding effort (so I think at least).