Except for HPDT (High Performance Desktop) Segment (AMD has taken the performance, efficiency, and and price-performance crown now, and Intel is just less stuff for more cost), Everything (and Everyone) else IS moving to ARM.
Apple has its iPhone, and and iPad segments on Custom-ARM chipsets, and soon Macs, the and MacOS will be transitioning to Apple-designed Custom-ARM chipsets. That's a boatload of the "Creative/Content/Arts" Device Segment.
Microsoft is, with the introduction of the Microsoft-Designed Custom-Arm SQ1 Chipset in the Surface Pro X running an ARM64 compiled version of Windows 10, the upcoming Android-based Surface Duo will likely have either a Snapdragon (Qualcomm ARM Chipset) (likely an 8cx or the Microsoft-Designed Custom-ARM SQ1 Chipset)...
Future versions of Windows 10 (based on CoreOS and having better operability with a Read-only OS, the and Sandboxex App Environments) will also be on ARM64 natively.
So, let's see if Apple is moving to a let's say 90% ARM Chipset based device ecosystem, Microsoft is transitioning Windows and future-facing devices to ARM64, and "the rest" of the world's devices that don't run AMD/Intel x86-64 are ALSO running ARM64 on ARM-based Chipsets, shouldn't Serif ensure that ALL OF THOSE DEVICES can run a version of Affinity (Suite) apps on them?
Otherwise, why bother?
Serif does have a bit of time, but the Surface Pro X (first ARM64/Custom ARM Chipset based Surface device running Windows On ARM) has launched, the Surface Duo isn't launching until Holiday 2020, we don't know if the Surface Neo will run on ARM, but AMD, and or Intel, and the Surface Pro X is the first in a "Category Example" for PC Makers of a 2 in 1 Convertible PC running Windows On ARM natively on ARM64 on an ATM Chipset, and signaling that their iterations are now welcome, but and expected.
One of the 2 new "Dual Screen" category of Surface Devices will at least run Android on ARM, future Microsoft and PC devices will be running Windows On ARM and do so natively compiled for ARM and ARM64.
Samsung. They already have a new ARM based Laptop running Windows On ARM. Their Android Phones run on Samsung-designed Custom-ARM Exynos, and and Qualcomm-designed Snapdragon ARM-based Chipsets. Their S Pen Stylus-equipped (4096 to 8192 levels of pressure styluses) Note series is huge, but and a huge number of stylus-equipped devices to take advantage of for Serif, and the Tab S series of S Pen stylus-equipped Android-based Tablets... And soon with the Surface Duo, the Android Tablets with Dual Screens that can leverage the Surface Pen or Surface Pen X On ANDROID!
For Serif to ignore the very fertile ecosystem developing for ARM would just be a titanic failure of leadership and engineering.
Besides, the Affinity (Suite)/Photo is almost missing the GOLDEN OPPORTUNITY to position itself as THE premiere Photo Editing Solution on Android (with whichever Stylus the artist prefers: Apple Pencil, Surface Pen (X) (all the protocol-compliant Third Party Styluses that are compatible with the Surface Pen besides Wacom's Styluses), S Pen in many iterations...
I think it would be foolish for Serif to miss such a timely opportunity.