There is a new kernel snap (version 4.4.0-109.132) for Ubuntu Core devices to address CVE-2017-5754 (aka Meltdown). It will get pulled in automatically on Ubuntu Core devices via the automatic refreshes.
The downloadable image of Ubuntu Core will also be updated shortly to contain this updated snap.
The names are: pc-kernel, pi2-kernel, dragonboard-kernel. The process/release is done by the kernel team. AIUI they do publish to beta first and then get get HW CERT to validate the kernel. If that is complete it goes to candidate and stable. Might be worthwhile to look at/discuss their release policy in detail with them.