TYPO3 Core

Patch set 6 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/61511

Patch set 7 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/61511

Patch set 8 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/61511

Patch set 9 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/61511

Patch set 10 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/61511

Patch set 11 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/61511

Patch set 12 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/61511

@Benni Mack

Suppose we have a news plugin with 12 custom display modes. This is a real life scenario. Currently the plugin uses switchableControllerActions. This deprecation means that instead of having one plugin with 12 selectable modes we now need 12 separate plugins, right? Does that really sounds well thought and reasonable to have a plugin selector go beyond horizon vertically?

I must say, I agree with @Dmitry Dulepov here. A custom plugin for each view of each extension could potentially result in around 20-30 plugins in the content element selector, and I imagine this would be quite confusing for editors and admins alike.

Please have a look at my post, explaining a few things in detail:
https://gist.github.com/alexanderschnitzler/c685218feea1a8956cc3f915f7a08d0b

TLDR;
No, you don't need to create a single plugin for each controller/action combination, only for those entrypoints where controller and action params should be hidden in the url.