Hey there, Ionic Framework has not released major version 5, you are seeing the Ionic CLI release.
Ionic CLI
The ionic package is the Ionic CLI 
ionic - npm
The CLI is used to start & serve Ionic apps, but does not contain any changes to the framework. You can see more information on the CLI installation here: How to Install The Ionic Framework CLI to Build Mobile Apps
Here is the changelog for version 5 of the CLI: https://github.com/ionic-team/ionic-cli/blob/develop/packages/ionic/CHANGELOG.md#500-2019-05-29
Ionic Framework
There are a few packages that make up the Ionic Framework which is used to get the components you see here: UI Components | User Interface Application Building Components
@ionic/core: contains the core Ionic UI components that can be used in a vanilla JS application https://www.npmjs.com/package/@ionic/core
@ionic/angular: contains the core components & bindings to work with Angular https://www.npmjs.com/package/@ionic/angular
The following packages are in beta
@ionic/react: contains the core components & bindings to work with React https://www.npmjs.com/package/@ionic/react
@ionic/vue: contains the core components & bindings to work with Vue https://www.npmjs.com/package/@ionic/vue
You can see more information on using and updating these packages here: Ionic Framework Packages: CDN, Angular, Vue, and React
Release Schedule
We have some documentation on our versioning here: Versioning | Ionic Documentation
A major release will be published when there is a breaking change introduced in the API. Major releases will occur roughly every 6 months and may contain breaking changes. Several release candidates will be published prior to a major release in order to get feedback before the final release. An outline of what is changing and why will be included with the release candidates.
This means that we will not release a major version except for at a minimum of every 6 months. At the moment we do not have a major version planned in the near future, but there will be a full list of any breaking changes as we had with version 4.
We have been releasing every 2 weeks to quickly get bug fixes and features out.
Release Notes
We recently published a document that outlines the Ionic Framework release notes here: Release Notes | Ionic Documentation
If you are looking to see what the latest framework version is, that page is updated with each release.
Documentation
I hope I cleared up some things, but if you have any ideas for how we can improve the documentation to make this better known, please file an issue on our documentation repository: Issues · ionic-team/ionic-docs · GitHub
Thanks! 