Doing so can greatly speed up test runs since fewer available test runner threads are blocked by the ExclusivelyUses-TestRunner tests.

in my case I have one machine with 12 MaxProcessingThreads and one with 4. Yet NCrunch runs virtually all of the Exclusively-Uses-TestRunner on the machine with 12, wasting a ton of resources and really slowing down runs.
I can hack around this by refusing to run these tests at all on the machine with 12, but that is quite suboptimal as that machine then sits idle doing nothing when there are only such tests in the pipeline, and when the other machine is not up the test runs just hang.

I'd love to see this implemented. I'm sure I'm far from the only one running a grid who would see a major performance improvement from this!

Cheers :)