4.0 as far back as 2016 was labelled the version where they would add a second system. We see CIG not being able to do this, and even LittleAnt suggested that if the tech isn't ready they may add the second system via a main menu option rather than in-system travel.
I still don't get why they couldn't just do a bog standard server switch for a second system, behind some sort of fancy animation, just to be able to brag it's there. Whatever they do will end up being caveated with all the usual "tier 0" excuses anyway, so why not just hack a quick and dirty "temporary" solution like with literally everything else in the game?
That SSD requirement makes me think a little comparison. I happen to have RDR2, and can run it with quite high graphics settings due to me having RTX2060. Now then it is installed on HDD. Works without problems. Only difference between SSD and HDD install is loading times. Tells me something about quality of work I say.
RDR2 is also Vulkan-based, I wonder why CIG claims to be waiting "until Vulkan ships". Sounds to me like they're waiting for Amazon to do the heavy lifting and add it to Lumberyard for them.