Think I'd go with not changing engine, that kinda includes not overhauling either.

Even if you do it for this year's shiny, everyone will just want it again for next year's shiny.
There's a reason it decimates release dates when indev projects change engine, nothing works properly for ages after doing it.
Shadows do need attention though, they pop in/out in a lot of places like icy rings and megaships, spire sites worst of all.
Not sure why but rotational correction also changes all shadows cast within starports.
I'd remove all attempts at antialiasing, fix projectiles invisible without bloom, then work on shadows.
Secondary goal - soften nightvision because it glares on all the extra edges and model detail added with Odyssey.
This is kinda connected to shadows, everything used to be brighter and didn't need nightvision as often.
Would be good if it just didn't highlight anything if already bright, would also stop it overriding docking pad holos.
Also shouldn't highlight anything inside ship unless pilot visor is deployed - this actually works perfectly on foot but doesn't map properly when in a ship.