Consistency? Elite Dangerous? Bwaahahahaahahaahahaaaaa!!!!
For me there is a fairly consistent rule for these - it's just not one which makes any in-universe sense whatsoever, so it appears completely arbitrary.
I think the idea is to get - roughly - the old Elite "save at stations" experience in a MMO where you can quit-and-resume anywhere.
So:
- ranks, rep, credits, data, materials. The vast majority of these, in most circumstances, will come from your previous trip(s) ... so you keep those when you 'reload' (and get to keep the ones you picked up on this trip as a simplification)
- cargo, discovery data, bounties, bonds, vouchers. The majority of these are picked up for a single trip and handed in when you next dock, so if you don't make it to the next station, you don't get to keep them. (You lose ones kept over multiple trips, but it's easier to be consistent)
Crew I would agree belong in the "multiple trips therefore you keep" rather than the "single trips therefore you lose" column, though.
Multicrew telepresence is basically how I expected "Elite multiplayer" to work in a "wouldn't it be great if" sense back in the 90s - you'd have someone's singleplayer save, and you could connect to that and fly along with them either as a turret gunner or fighter escort using their funds and resources, and then at the end of the session they'd just carry on as before ... because it would have been impossibly inconvenient to sync up two savegames in space and time before connecting them. This is way before "persistent MMO world" was a plausible solution, of course.
(Personally I wouldn't have tried to come up with an in-universe explanation for it at all. Just pretend they were there all along but not on the bridge earlier)
On synthesis, I think replacement SRVs and SLFs should be synthesisable - though SLFs would need to be slow to avoid breaking combat balance and both should be fairly expensive. Making SRVs synthesisable will also stop FDev getting thousands of "my SRV mysteriously exploded" bug reports and Support calls when DW2 sets off: maybe that will encourage them to do it?
