Will lede update the kernel version to the next lts kernel (4.14 ?)
Yes, probably.
The next stable release is most likely going to use kernel 4.9 for most targets. I guess kernel 4.14 after that.
Some details on the mailing list:
http://lists.infradead.org/pipermail/lede-dev/2017-October/009124.html
i was talking about trunk... didn't know stable was stuck to 4.4
Should apply to trunk too.
It's most likely going to be:
Add support for 4.9 to targets still lacking it in trunk -> make new stable branch for kernel 4.9 and release it -> start adding support for 4.14 in trunk.
My guess is trunk will still be on 4.9 through 2018 at least (since ther will still be support even tho it's EOL), 4.14 most likely not before 2019 / 2020.
I'd be happy to be wrong tho ;).
Well, ask yourself: how would a stable release be stable if you switched between major kernel releases?
Like @hbr said the next stable release will be on 4.9 probably, and the one thereafter on 4.14, both LTS kernels, like 4.4 is.
I saw one of the devs working on preliminary support for 4.14 on lantiq, and no doubt others will follow, but it will take a while until it will be widely supported (ar71xx only switched to 4.9 a few weeks ago afaik, and similarly ramips hasn't been stable on 4.9 for that long either).