That's all well and good.
But does the mapping, and indeed the routing software, actually care about that level of accuracy.
Take driving off a motorway intersection. My sat-nav is always convinced I've continued onwards until, quite literally, I'm off the motorway by some tens of meters. The software cheats and just assumes you've followed course until you hit a big error margin at which point it's willing to accept defeat and recalculate.
How are you going to utilise cm-level accuracy without a) bugging the user because he drifted slightly left or b) having to "debounce" all the location logic so it doesn't make decisions based on tiny variations?
"Better signal" in difficult locations is great. But the accuracy thing is a bad sell.