Currently. as far as I understand, the code get's the gateway using a filter that only get's the gateway if the route if an ipv6: https://github.com/libremesh/lime-packages/blob/fa205c64c8630d07cfeacdf27173a68e3dd02a2c/packages/ubus-lime-metrics/files/usr/libexec/rpcd/lime-metrics#L110
It should work also when the gateway doesn't have an ipv6 address.

For normal builds, it is helpful to have more specific versions than simply the upcoming version snapshot. 2019.2.MMDD.HHmmSS.0 seems like a reasonable format. It combines the year major and minor open source versions with a timestamp and ending in .0 which follows an internal convention where these are treated specially as development builds.