Mark Gurman, writing last week for 9 to 5 Mac:
Apple is currently planning to use the new system font developed for the Apple Watch to refresh the looks of iPads, iPhones, and Macs running iOS 9 “Monarch” and OS X 10.11 “Gala,” according to sources with knowledge of the preparations. Current plans call for the Apple-designed San Francisco font to replace Helvetica Neue, which came to iOS 7 in 2013 and OS X Yosemite just last year, beginning with a June debut at WWDC.
I’m finally getting used to Helvetica Neue and Apple’s already switching to a font I’m not yet sold on. Maybe I’ll be all in once I spend some time with it, but for now I’m cautiously optimistic.