It would probably take a decent while for sure and ultimately it's a decision that the accountants will take as much as the game developers. Faced with the possibility of releasing a badly hacked together version of Odyssey for eight year old consoles though, they're likely to look at whether there's enough money to be made from a better version designed from the ground up for current generation gear, on the basis that the takeup of that gear (and therefore the potential market) is only going to increase over time, whereas the last generation is going to mirror that with a decline.
Obviously, the other side of the calculation is that they may determine projected sales wouldn't be enough to make it viable.
I certainly can't see how a PS4 version is ever going to happen. I'm basis that on my own experience with Odyssey on PC - my PC is
very old (eight years by an amusing coincidence, like the PS4) and has an i7 3770 with 16 gig of RAM. I do however have a more modern graphics card than you'd expect in a machine that old because my old one blew a while back and I replaced it with a 2060.
Here's a comparison between my
ancient CPU and a PS4 Pro:
Comparison between Intel Core i7-3770 and AMD Neo (PS4 Pro) with the specifications of the processors, the number of cores, threads, cache memory, also the performance in benchmark platforms such as Geekbench, Passmark, Cinebench or AnTuTu.
gadgetversus.com
Scroll down to the 'performance' section.
That ain't good at all and you need to bear in mind that on top of that, my 2060 also knocks the living crap out of the graphics hardware in a PS4.
Guess what performance I get in Odyssey with that rig?
Around 60fps in concourses, less in CZs,
at 1080p without using supersampling. And you could use my PC as a room heater whilst it's doing that. That's after
eight Odyssey updates,
five months after release. So realistically, no matter how much optimising they do, I just can't see how they're going to come up with a version of Odyssey that can deal with 60fps @ 1080p on last gen console hardware.
That's why I'd think there's hope for you for a native PS5 version - because I really think the tech issues will take anything other than that off the table before the game has even begun. Like I said, it will depend on how much money they think is in it in terms of sales, not only of Odyssey but whatever comes after it. If they see this as the last update to Elite then yeah, it might well be over for consoles. If they see Odyssey as a platform on which future content (and sales) will be delivered, it may make sense financially to take the development hit now and make a version for current gen consoles.
That obviously wasn't FDev's intent back when Odyssey was first announced, they'd clearly intended making a last-gen console version only but as John Lennon said, life is what happens to you whilst you're making plans.