Ive been interested in this sort of thought for quite some time, as an avid OSM user (I use it essentially exclusively for all my map needs) and sometimes contributor (I've contributed some information in areas I've lived, and a couple of interesting overlay maps in the US). I do not use Facebook at all, nor any of their products, so that isn't really a draw for me.

I've found that OsmAnd for street navigation works as well as and in some cases better than Google, particularly semi rural areas. The big sticking point with using OSM for car navigation (the biggest use case for any map framework and/or app) is address lookup. Usually Nominatim is used, and particularly in the US it doesn't give you any address data, only cross streets, so navigating to a place you have no idea where it is means you're going to use Google or something else to find it, and then use OSM to navigate out of principle. This is a major roadblock, if you've got to use Google to find out where it is, you'll normally just use it to navigate as well.

I have a solution to this problem, and that is to source address data from openaddresses.io (a collaborative, open source geocoding project) for address lookup. It will require a bit of work to do, specifically on Android, I will have to build an address lookup backend alternative to Nominatim that sources address data from openaddresses.io, which requires account registration to download geocoding data, which means that it will probably require local storage and lookup of data. Once this exists though (and I have not started building it, I tell myself I will but I have other things going on) you've essentially eliminated the big friction point with OSM and it becomes a viable competitor to proprietary navigation in cars or otherwise on roadways. I think if this were built, and the word got out, it would kill the Google Maps monopoly over consumer use, at least with the "sick of google" demographic, which is sizeable.