Aside from separate server suggestion, "IF" devs incorporate MP, fleshing out MP would be a monumental step requiring a robust infrastructure on the backend. While I see the devs developing the code, to fully implement the MP aspect, a third-party would be ideal that is well versed in bringing MP loads and frontend frames per second (fps) to end-users at reasonable rates.
If the global community is segmented by region, or country, MP is possible. Otherwise, if the entire global community is in one node, disaster will follow. MP, if it is to be included, must begin designing, developing, and testing user loads now- not later.
As for the granular aspect of MP:
1. Co-pilots
2. Passengers
3. Last Save Last Respawn
4. Death Respawn Penalty
As for roles, building, flight, maintenance, are fairly straightforward. In the KSP2 world, unless these roles are coded as OPTIONAL, MP is a glorified tourist.