When talking about the core components we mean things like buttons, text field, switches, tooltips, etc. These will be updated to newer, completely rewritten versions.
We already have components for this but they are old and lack some features we want. Due to the way the old components are built those features can't be added easily.
More core components will be created over time but each one added will bring up the quality of the site a bit more by looking and feeling better than before.