This article is mostly speculation (although based on rumors from reliable sources), but they do speculate that the "pro" level machines will stay intel for a long while.
Fat binaries with slices for each architecture, much as was done for 32+64 bit x86 and is still done for iOS. Porting x86-only code to arm can sometimes be a lot of work, but supporting both x86 and arm at the same time isn't any more work.