In my tests, the burst shoot in RAW mode on the Z1 did not speed up the bracketed shots to below 6 seconds.
See this test:
With the Z1 using DNG/RAW images, I can only reduce the time down to 6 seconds. If I try to go lower, it will not take all the images.
We could continue development of that branch to meet the requirements in this thread and publish the plug-in specific to Z1. However, I do not think it will yield the desired result. At least not with the current technique we are using.