Odyssey has brought some cool options, like flying shotgun in person in another ship or driving other people's SRV. Flying together needs some work as instancing often kicks you out when entering/exiting supercruise, but if we can ride a ship, why not let people exchange ships, so they can try out what their friends fly?
Main problem I see with this is the guy who borrowed the ship needs it back so he kicks out the other guy and needs to get it back. In a game like Gta online it is not a big deal as there are many ways of transport, you have a mechanic to call your car back and the map is tiny compared to Elite. This could be solved by an unlimited Apex taxi that will take you anywhere on the map you want, or a ship delivery service that brings it to your current planet. I'm talking about a long exploration journey in the deep space. But on the other hand this ruins the immersion of being in a undiscovered uninhabited wasteland.
Other much more minor change I think is worth pursuing is to synch ship interiors when riding shotgun, so you can see some of the pilots instruments and the various bobbleheads and lights. Would be a lot nicer than a dark interior with only a limited hud.