... if there is a new version of Elite for PS5, whether our full account will transfer over, because it would be a different version of the game built to run on a far more capable console.
That's the game engine, i'd be highly surprised if their player data has a dependency on any sort of codebase;
worryingly surprised really.
One would assume the core player data between PC, xbox and PS4 are exactly the same, with additional tables to hold platform specific information.
If the 2020 version uses a different database schema, the obvious thing is to do a data migration to convert current player info over (including consoles). Likewise cross-save player data shouldn't be particularly difficult if they've designed and built things correctly (just the data I mean, not netcode, engine work etc).
Unless they want to force a reset, so everyone starts from scratch again: which would resolve things like legacy mods, players with years of glitched credit earnings and so on.
Really it's much like platform holders for years saying crossplay was impossible: as long as the netcode uses compatible APIs each platform could have wildly different engines, but talk to each other. Passing a player's location data and state can be coded for if there was a will, and then developers like the Rocket League guys flipped a switch to proved it was practical too. The issue was platform owners trying to protect their environments, not technical (well, and handling things like Steam Friends lists interacting with PlayStation ones).
Games which do cross-save, like Helldivers doing PS4 <-> PS3 <-> PSvita, show different engines and hardware can do cross-save (and cross-play).
Anyway, I guess we'll find out, but I personally am not expecting a PS5 version beyond a PS4 port, and more that the 2020 version is fully PS5 compatible.