I’ve collated some of the comments over the last year of extra ideas and observations that might be useful to the overall consideration.
Collated ideas
“But maybe in MSFS2020, there should, be some Built In Voice Communications for pilots in a Shared Cockpit plane, which is really necessary, rather than having to rely on some random 3rd party voice communication system, like Discord, Teamspeak ? or other.” - N6722C
"I posted a suggestion here some time ago about about there being two different kinds of shared cockpits that MSFS could choose to support in the future:
- Pilot + copilot / crew, i.e. multiplayer shared cockpit.
- Pilot + passengers; passengers using a free demo version of the simulator. (See Passenger-version of MSFS to break the isolation 12)" - Btmnstr
"My Copy/Paste wishlist for shared cockpit functionality:
- SDK support for 3rd party ( more complex aircraft like PMDG / A2A )
- All aircraft functions / switches work for both players
- Hot key / Request & Accept for switching Flight Controls
- Flight Control Override for Host ( host can force control switch from other player )
- Quick “Player Kick” function ( if some clowns starts shutting down engines and systems )
- Voice Com - Hot Mic for players in same aircraft
- Positional voice com - volume / direction depending on seat
- UI for selecting Player Seats
- Players should be able to switch to any empty seat in-flight
- Add more than 2 seats for Shared Cockpit (So other players can jump in jot just pilots)
- Cockpit Jump-seat / Flight Engineer Position ( depending on aircraft )
- Passenger Seats
- ‘Lock’ Seats ( players should not sit in the same seat position )
- Add 3D Avatars in correct seat ( so players can see each other )
- 3D Avatars should track head position correctly * Pilot flying should have hands on yoke / stick?
- Sync Time of Day / Weather ( LIVE mode - but for host’s settings ) for players
- ( Join in Progress ) functionality would be nice
Waaay down the road, it’d be cool to have FPS-style player aircraft walkthroughs, and the ability to leave the aircraft on the ground and do a “real” walkaround, or start outside the aircraft, etc ( walk anywhere within the airport fence? )" - SPERABrentH
“And more advanced features to help in the cockpit could be added, such as a visual pointer that would show a specific button/switch that both pilots could use and see, or even just support for more than 2 people in the cockpit (with modes like captain seat, copilot seat, view only seat).” - FlyingCookie650
Regarding how long it has taken - in 2020 this guy said this:
Oh yes, good to hear they are at least planning this feature. Can’t wait. So hyped 
"
I just put this down because it shows there has been a long time since this has been planned.
“There should be a warning or error for incompatible Airac / Navdata however, that’s the only thing I could see that may be causing problems.” - NixonRider
"Interesting note on realism “It’s MANDATORY to fly this beauty (the PDMG DC6) with a a copillot to obtain the maximun performance and all this mighty plane have to offer.” - Delihus
On 3rd party plane compatability:
"Unless Asobo is able to come up with some incredible system that can carefully filter out per-frame updates of local vars (which is certainly possible and I wouldn’t bet against them) then there would probably need to be some kind of rating info in the marketplace for every 3rd party aircraft, like:
- basic multiplayer compatible only (usual native items synchronized, gear, engines, control surfaces etc)
- enhanced multiplayer: all external moving parts synchronized (doors, hatches, cowl flaps etc)
- shared cockpit compatible: all of the above plus full cockpit synchronization" - Ramasurinen
“Second, there must be an option for a ‘private’ server session so that only invited players can join. Nothing more annoying than some 10 yo buzzing your plane with an F 18!!”
Cheers