I maintain a map style that shows various sorts of milestones - here’s one: https://map.atownsend.org.uk/maps/map/map.html#zoom=19&lat=52.994227&lon=-1.39447 . Those tiles only cover the UK and Ireland, but you’re welcome to use that map style for elsewhere if you want to.

If you want to search for stuff, the taginfo site can be pretty useful: https://taginfo.openstreetmap.org/tags/highway=milestone .

The normal answer to the questions of the type “how do I suggest to OSM to do X” is “create an example yourself to do X”. There are many more good ideas than people currently doing admin for the main OSM site, so most things get done somewhere else first and if they’re a good idea, get incorporated.