I think that's an overestimation of the capacity of the Apollo INU. They used star sighting for updating the orientation and location of the spacecraft as well as ground based tracking. The INU was used as a controls input but was not left standalone and uncorrected for the entire flight.
In the intervening time the main change has been to replace mechanical gyros with lasers, particularly fiber-optic systems, and with MEMS devices to drop the size, power, and cost. It's likely that precision could go up, but unless there is some system need for it the other drivers are more important. GPS has removed much of the need for long term stability and it's possible to build detailed terrain maps to manage a flight path over land that doesn't require an inertial reference. I can also imagine a system based on passive reception from cell towers to manage position and orientation information within a few meters. From my understanding a street mapping effort also mapped Wi-Fi as well - that could also be used for location. I'm sure some 3 letter agencies already have tech to do that.