The boot arrangements for legacy and mainline kernels are completely different so attempting updates is just asking for a pile of support issues, so a forced reinstall is the best option. It's no problem to backup and restore Kodi data between versions as that doesn't change much, although if the backup contains binary add-ons you'll see a list of add-on "fail to start" errors until newer versions are downloaded and updated. That's nothing new though, it's the same as any LE major-version update.
The main idea we've asked the Availink folks to grasp is; if they develop something that works on the Amlogic 4.9 kernel today they will be screwed in the future when Amlogic bumps to 4.19 (or god forbid, something newer) and they will never get it upstream to the mainline kernel as it won't follow kernel APIs and coding standards. However if they create a driver that runs on the mainline kernel today, they will be free to add whatever hacks are needed to backport it onto Amlogic bsp kernels (as no rules apply there). That's been understood, and we also persuaded them to relicense the driver under GPLv2 instead of something proprietary and restrictive.
So things are progressing and I'm able to compile the Availink demod (or an earlier version, I didn't rebase on it for a while) but it's still early stage and only one of several components needed for DVB support. Work also needs to be done on the tuner drivers that are used with their demo, which exist in various forms (not all have good prevenance for license and future upstreaming) but these needed to be deconstructed and adapted into independent modular drivers; the Amlogic kernel compiles them into a single monolithic blob, which is meh. Then the major missing piece is a new V4L2 demux; the mainline kernel has a completely different DRM architecture so we cannot repurpose code from the Amlogic kernel. And finally if we get that done, it should all be describable from device tree so that different tuner/demod combos work without special compiling. The availink folks are not completely sold on the whole story yet, but if we can at least get their demod and tuners to build alongside a new demod, the rest can take time.