For me it would be to have a similar behavior like when VS is building in cases when the user executes an action which takes some time to execute and modifies a lot of code/project files.

One example would be when working with nuget:
- Update-Package (-reinstall)

I would love to have a big "Pause all" button as well. With roughly 30k+ tests in one solution it brings development to a crawl (and often crashes, or freezes VS forever, requiring a restart). Sliding build delay helps a bit, but is not the same. Disabling/Enabling is what I currently do, but is very slow.

Note that internally, such feature already exists, when NCrunch pauses its build (even right in the middle) while Visual Studio is building.

It would be nice to combine both.

My use case: Sometimes I have some bigger refactorings or it is done on classes which cause a lot of expensive unit tests. Until I am at least somewhat done, running the unit test makes no sense. Since these are bigger changes, I save (several times) before I am done.

Currently I handle this by switching to the "Run all tests manually" mode and then switching back.

What's the use case for that?
Sliding build delay, or this feature: https://ncrunch.uservoice.com/forums/245203-feature-requests/suggestions/6401826-option-to-build-and-start-running-test-only-on-fil , would that address your need?