Dark Souls 3 for Mac certainly won't arrive before Dark Souls for PC, and that is due to get a release date in early 2016. If Dark Souls 3 for Mac is in development, we wouldn't expect to see it prior to the later part of 2016, and more likely 2017.
If you can't wait that long, then consider installing a copy of Windows 10 on your Mac using Boot Camp. We often joke that Macs make the best PCs, and you will then be able to play Dark Souls and other PC games directly on your Mac.
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