What if I prefer a predictable release cycle for the base OS, but still need the latest LibreOffice/VLC/_____ for one reason or another?

I like the approach taken by e.g. Nginx and MariaDB, where I add additional vendor repositories, but this workflow is probably neither user-friendly enough for my mom, nor have all vendors the resources to maintain several repositories for different distributions and their respective versions.

Use an OS with backports, like Debian. For example, if you took Debian Jessie, you could pull LibreOffice 5 from backports. VLC is already almost up-to-date (2.2.1).