I doubt Unity will investigate this avenue in the short or long term. The idea is simple, but there’s probably a lot of places that expect assets to be loaded. So it’s not just about adding an option to skip loading a subset of assets in a project, it’s about finding and fixing all the places that subsequently break.
And Unity is already invested in other approaches to alleviate the slowness in big projects: One is the switch to CoreCLR and with it from domain to partial code reload. This should improve the time it takes after code was (re-)compiled. Another is a switch to on-demand async asset importing, which should greatly reduce the time spent waiting for the editor to import changes.
However, both of these are scheduled for a release after Unity 6, so it will take a good while until these will benefit production projects. In the meantime, as CodeSmile outlined, all we can do is the grunt work of optimizing existing projects and making sure they don’t degrade.