Hi Andreas,
Yes, the implementation part is where I'm lost at the moment. I'm wondering if there would be any interest from cemetery managers to agree to adopt Plus Codes as a standard. They could still use whatever Section/Row/Plot system they have now, but simply add the Plus Code. You touched on the advantages in that regardless of how the cemetery might be redesigned. Maybe we could think of Plus Codes and cemeteries as your final, permanent forwarding address.
For modern cemeteries, I would think that they could provide a simple lookup by name, date of birth or death, etc. They could then include the plot information and the Plus Code. I'm thinking of a race I just ran and the lookup information for the finishers; enter one or more qualifying bits of information and get the results.
For older cemeteries, or those not actively maintained, projects similar to what
billiongraves.com is doing could be encouraged. In fact, since
billiongraves.com already has GPS coordinates, adding Plus Codes to their data would be relatively easy.
I think the best solution would be to encourage cemeteries to adopt the Plus Codes as a standard. Implementation would be on the local cemetery level as I think that's where it would be most frequently used. Most people searching for a grave probably know which cemetery. Cemeteries would then be encouraged to make their information publicly available and shareable through sites like billiongraves or various genealogy sites.
If anyone has any contacts with cemetery managers or their trade associations, it would be interesting to get their input. However this would be implemented I imagine it would have to be at almost zero cost as I'm sure they don't have tons of resources. However the standardization and permanence of the Plus Codes should have some appeal.