Are you aware that I already massively reduced the time required to make improvements? It takes only 1-2 turns for most common improvements now. You can already get ways of speeding up workers in the game currently (wonders, policies) if that is important to you. With a couple of these, it might reduce even the 2 turn improvements to just 1 turn. I could decrease worker speed further easily enough with certain technology markers, yes. If anybody has played with this mod on far enough to have specific suggestions, let me know.
I gave the workers speed 4 to begin with, and with roads and railroads they should be able to get around relatively quickly on land, at least. I don't know how I could go about speed them up even further with tech or eras. You can speed up embarked movement, and you can speed up entire "domains" (land/air/sea), but I don't know if I can speed up a specific unit. I would probably need to introduce faster modern versions of workers, as some other mods have done.
It might be more playable with a limit of 2 workers instead of one. That's easy for anyone to edit in the mod's xml.
Any major system overhaul like this public works system will definitely require modding access to the C++ codebase, which is supposed to be made available in the future.