I'm thinkig about switching from Kubuntu to KDE Neon and I would want to know how long it will take until KDE Neon will be based on the new LTS release of Ubuntu which will be released soon. I don't want to switch to KDE Neon and then have to do a distro update to get the new version.

Going by the past two LTS upgrades in neon, it likely will happen near the end of this summer, at some point after the first Ubuntu LTS 'point' release is out in July.