It will most likely kill apple laptops as a developer platform.
Unless you are deeply disconnected from the hardware, CPU architecture does matter. Most developers using macbooks I know have VMs for either Windows or Linux works.
It might be conceivable to use the ARM port of , or the ARM version of Windows 10. But it would also require a good desktop virtualization solution for ARM. If Apple release its own solution or creates a partnership with let's say VMWare to release something at the same time an ARM macbook comes out, it might work, but barely, and I'm not sure if developers are at the top of Apple's priority list. In the end, with the Linux subsystem in Windows, choosing Windows as a development platform might make more sense.
As a side note, if Apple switches to ARM, I foresee a lot of cringing. The switch from ppc to intel was annoying for a lot of Apple users at the time, but there were a lot of goodies (bootcamp, better autonomy, better performance, VMs) that kind of made it up for it, basically, nothing was lost in term of possibilities, a few were actually gained, and only the transition was a bit painful. With a switch to ARM, you may gain a little in term of autonomy, but with macbook pro already at +8 hours (~a work day), not sure it's a game changer, at best you will stay the same in term of performance, and you will lose in compatibility with other OSes.