There have been some experiments, but nothing with any realistic hope of software support. There’s also a big table on the wiki envisioned as a source for routers to intelligently backfill missing speed limits on demand. For maintainability, the table is limited to national, state, and provincial laws, so it’s of limited use in the U.S., where local laws often matter just as much. This scraper turns it into something more digestible, but it has some limitations because many speed limit laws are vague and even subjective, not intended for machine readability.
There’s a relevant discussion in the StreetComplete project with respect to Austrian citywide speed limits and, since I was asked, American ones too. As in this case, cities in some U.S. states commonly post “citywide” speed limits that are redundant to the state’s laws about cities, but it’s still useful to explicitly distinguish this situation from cities that raise the citywide limit above the state norm, and of course from those “otherwise posted” limits.
So far, the most common approach in the U.S. and probably Canada is to simply tag every individual street with whichever speed limit applies to it. If you start by blanketing the city in speed limits before meticulously documenting all the exceptions, then maxspeed:type=* is useful for clarifying the basis for tagging the speed limit in the first place. Otherwise, most mappers assume the street got individual attention and may unfortunately defer to whoever tagged it originally, despite more specific observations.