Assuming you get as far as actually having code in one repo, the advantages of monorepo do not come for free. You either use a consolidated build system or you're still linking code using packages. A mono-build is no small task especially if your org is of any sort of complexity.
You'll almost certainly never get away from packages entirely unless you want to pull in the source code of all your dependencies. Not only are you merging it in but you're integrating it into your mono-build system. Doesn't sound feasible or enjoyable to me.
Some people consider mono-repo a fools errand. At most places you can take the pragmatic approach of consolidating repos where it makes sense while keeping the decoupling advantages of packages where it makes sense. They both have trade offs.