As previously mentioned, the GeoPackage SWG has been investigating an extension to support tiled, gridded elevation data. A year later, we are pleased to announced that we have completed our work on this extension and that we intend to release it as part of GeoPackage 1.2. This extension will share the mechanism used in the tiles portion of the standard.
The extension description describes the metadata tables needed to manage elevation tiles and encodings for the elevation values themselves. The extension supports two encodings. Most users will use the PNG encoding which uses 16-bit integers. An optional scale and offset allow for more efficient use of the 16-bit space. For those users who require greater resolution, there is a TIFF encoding which uses 32-bit floating point values. For convenience, we also provide abstract tests and table definition SQL.
To ensure that this approach will work, we conducted an interoperability experiment. In this experiment, documented in an Engineering Report, a number of participants produced GeoPackages containing elevation data and ran visualization and/or analytics on them. The experiment exposed a number of issues that the SWG subsequently resolved. At the OGC Technical Committee meeting in February, the SWG voted to add the extension to the standard. Do you think it is ready?
 Note: this post has been updated 8/20/17 with the permalink for the engineering report.