This will not just give us the ability to create JSON callbacks really easily but also for autocomplete paths etc.. too. I know this could be handled in Contrib but I think this would be really nice if we have this in views core.
Here is an initial patch that add the display plugin, and some basic tests.
I would like to add some options around the actual data that is provided in the JSON, first things first.
PASSED: [[SimpleTest]]: [MySQL] 50,754 pass(es).
PASSED: [[SimpleTest]]: [MySQL] 49,905 pass(es).
PASSED: [[SimpleTest]]: [MySQL] 49,807 pass(es).