Essentially what you propose isn't unrealistic technically, but it would still mean every telco, major and small clecs alike, plus all the hardware/software vendors would have to get on-board with an updated standard. I say updated because this is partially what the Phase II compliance was about trying to accomplish, although it fell short. I personally think this issue is more about people/companies and not about technology cause frankly the tech exists and isn't hard. It is politics and vendors refusing to agree because it isn't on their terms or where they can monetize it.
But even at that, all the PSAPS and secondary centers too would still require an upgrade because the software and hardware they use to convert calls and strip the meta-data would need to be updated. In some cases I think today it would require more flashes of equipment versus new hardware, but it is still a big change.
The voice option is interesting, but would hit a different type of issue, as it would require retraining of every call-taker and dispatcher, and would require significant system upgrades/changes still. Most times when you dial 911 in the US your call is routed to the nearest PSAP (based on the cell tower or physical address) then a call taker picks up the call and their first question is Police/Fire or Medical. Depending how you answer this your call is forwarded to either a dispatcher within their center or transferred. Many times these call takers have limited or no access to the CAD system from which your provider will be dispatched from, so they cannot add location data to a call. In other centers the call taker could do it, but it would still require retraining. Again, stupidity and politics is the problem here, not a technical issue.
On the voice option, while we have come a long way in predictive dialing for marketing purposes call pickup and voice recognition is still one of the hardest parts, so playing the location message at the proper time to not over talk or delay the call needlessly across all the various centers in the US would take a pretty significant platform and a lot of testing.
Last point, there are still a significant number of mobile devices that do not contain a GPS chip, which leads to the other problem, location can't be a standard around just GPS coordinates (yet). But most cell providers have the mojo now to use the towers to narrow your position quickly and automatically, another part of Phase compliance but the "area" they provide is still pretty damn big and doesn't make finding a person easy, but it at least narrows the area to search considerably. But how that gets communicated would all have to be agreed to by a huge number of people.
Personally, I think I'd rather be blindfolded trying to heard cats in a field, it'd be easier then getting telcos and existing vendors on the same page.