Most satnavs have it already.
- Satnav, is based on GPS which has a degree of error, it might place on a 4 lane road or a 2 lane road immediately parallel to it, with a drastically different speed limit.
- Satnav has no way of adapting to temporary lane closures or roadwork speed limits.
That's the reasoning for combining GPS with TSR camera data, in these 'intelligent speed' ADAS systems.
Waze is pretty good at this, presumably because the road/map data is crowdsourced